U.S. DEPARTMENT OF COMMERCENATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICENATIONAL METEOROLOGICAL CENTER

OFFICE NOTE 247

The Significance of Vertical Resolution for Predicting thePresident's Day Snowstorm of 1979

Joseph P. Gerrity, Jr.Development Division

NOVEMBER 1981

This is an unreviewed manuscript, primarilyintended for informal exchange of informationamong NMC staff members.

0

Introduction

In February 1979, an east-coast cyclone developed which caused a

very large snowfall to occur in the mid-Atlantic states. This impressive

storm, called the President's-Day storm, has been documented by Bosart

(1981), and has been the basis for a number of numerical experiments

with NMC prediction models. The storm was employed by Newell (1981) in

his study of the impact of sensible and latent heat transfer from the

sea upon the performance of an experimental ten-layer version of the LFM

model, and by Deaven in his evaluation of a new moist convection parameterization

system. Recently we completed a series of numerical experiments using a

variety of versions of the LFM model in order to isolate the relative

importance of resolution and physical process parameterizations in the

prediction of this storm. It is the objective of this paper to document

the results obtained and to propose a line of development which seems to

flow from these results.

At the time (18-20 Feb 1979) of occurrence of the President's Day

storm, the NMC was using the LFM II model described by Deaven and Newell

(1981), except that the precipitation parameterization system was still

that described by Gerrity (1976). The performance of the operational

forecast was critiqued by Bosart who rightly observed that the forecast

was insufficiently accurate to provide clear guidance that a major snowfall

was to be anticipated.

Bosart suggested that this relatively unsatisfactory performance could

be attributed to certain deficiencies in the then-operational model; viz,

1. inadequate vertical resolution

2. omission of significant level data in analysis

3. improper boundary layer physics

4. inadequate simulation of bulk effects of convective-scale processes.

The experiments reported here address to varying degrees the deficiencies

1, 3 and 4. Significant-level data are not presently available at NMC

in time for use in the objective analysis code. Future plans do call

for NMC to run a high-resolution forecast model with a later starting

time; this will permit the acquisition and use of significant level data

in the objective analysis codes.

2. The Storm

Figure 1 taken from Bosart (1981), shows the synoptic evolution of

the east coast cyclone during the period 1200 GMT 18 Feb. 79 to 1200 GMT

19 Feb. 79. In figure 2, also taken from Bosart's paper, the six-hourly

precipitation amounts are shown. The lower-right figure covers the six

hour period 1200-1800 GMT 19 Feb. 79, during which the snowfall intensity

was especially large in the Washington DC area.

In figure 3 we show the analyzed sea-surface temperature field used

in the operational NMC forecasts. The figure includes the difference

between the analysis and the RAND climatological norm for February.

Over a long strip, parallel to the east coast, the analysis shows sea

surface temperatures to be about 3°C colder than normal. Positive depar-

tures from climatology appear only off the coasts of New England and Florida.

This depiction is significantly at variance with the analysis shown by

Bosart in his figure 20. That depiction shows sea surface temperature

of 24°C off the Carolina coast which exceeds the RAND climatological

norm by two or more degrees.

Id

JULY 1981 LANCE F. BOSART 1543

w- W LI W- t- r r

Fka. 1. Surfce, 850, 500 and 300 mb maps for 1200, 0000 and 1200 GMr 18-19 February 1979. Conventional plotting and analysisscheme. Winds in m s-' [pennant - 25 m s-1, fll (half) barb - 5 (2.5) m s-r], temperature in *C. Heights, surface pressures andisotherms indicated by solid and dashed lines, respectively. Solid station circles above the surface indicate a temperature-dew pointtemerature swead , 5eC. Aircraft observations are entered on the 300 mb charts.

MONTHLY WEATHER REVIEW VOLUME 109

I; .Sa

I~~~~~~~~~~-- ~' '"<-~%'.~ ~..'~, t'/~. ~~...;.~~~~~~~~~

. oil - ...

S -~~~- '

S D S . f I a . ,, % .

'*'. . , , ,. ,,;,, -- ,____ h ia. I. (Continued)*'.."' ' . ;; * : . - _ ;:

a.

or

w i

%f

1544

441 ~ ~ ~ ~ ~ ~ ~ a

~:~ t ....I,, ,

.-",~, -;.

.. .'.I4

. I .

. '-

w .i WE~~~~~~~~~~tw'g*+-!~~~~~~0 "s

:>XU: ;~~~~~~~~~10 7

. _ _ _ _ _ . _oOf-w _ m c

~ -- i ~ re L .jR I

iI

I"

I

- w:,r ) yl,

or

...

.

m

Ir

LANCE F. BOSART

.:( . :: D:~' Li_**_or

L ~ ,-, ,.' '..~, ~~~,.~~~~~~~~~of,,

~~~-~. ''-~t,,b ,~10

'" ..,2 L _ __ - F7. h . i(.IIX~~~ , ... I.-':~~~~~~~.

,i

JULY 19811545

-F~~~~~~~5

q. . N " ( t' 'b ? -

.~~~~~~~~~~~~~~~~~~~S

I-,,

1"1'. t ': ,5 1- ': ' ' .: ' '

za " " ' " _ "

_ _ or

ct t',,

I

Ir

Bo WV _

.- : R I.

aI

I

Im

r

!fl

Pra-

ONw Ir

-., ~ , ': . .'X, o

a * * * * a . aidM A1111h

4a'e

Sh, Pc4fitk ItrI) u00oo0

or# s1-1-71

rr40

..- 'a4..

us.,a.

' ~~~~~~~~~~~~~Ji

.2%:

·'. i: .4,

*t aj Pi s.: :.a:

I.. -

-e

.i .

I I'

I0 :' '

:' ;t

' ,,, ,;. I-,,, I· :.'- .J;: s *r

',. .: rn-

. .? .,

.2 ,

* 1

. ' .N

.I \ o W 61el w . ia . ;.

-~~~~~~~~-N~~~~~~~~~~~~ -w~~~~~~~~~

I :,- . (wa OOOQtT t \ .so - 7 -.:.' .

tOk PmmimgI-)- .: , '1n

.?..I

1 9 % r-, I r I

, , ! *. -,

r . *.,

4 ' A' rm .~

' ,'E a -'* ' :

,: , . . ' ' m.,s.,"

, , , , .'.,z''''0,. 'i'..

*5.

* . ' . mu- st_ 's ' r1 v 7

Fmo. 2. Accumulated 6 h precipitation and present weather analysis for indicated times. Analyses in millimeters; raw observations for somestations plotted in hundredths of an inch (I mm = 0.04 inch).

0z-q

r* P<

:C*m

.q-4

hi

hi'C4-

4 'C0,Cx'i

.. .

I

"'I :~i~

·3 ~ .'::. ..

.,!

.

4. .

,. . .

-~~ c

oNATIONALWEATHER ERVICESEA:SURfAC~y TEMPERA+4RE X

U, -' 'ANALYSISv 4_ ,,1 FEB. ,91 9 ' "'

I PI , i-+

In figure 4 is shown an experimental regional analysis of sea surface

temperature produced by NMC's Ocean Services Group for the period 14-21

February 1979. The axis of warmest water runs from 80°W, 30°N to 75°W

34°N. The sea surface temperature in the warm-water streak is about

22.5°C except in its southwestern section where it reaches 24°C. This

objective analysis is similar to that presented by Bosart.

We are forced to conclude that the paramerization of air-sea inter-

action used in the experiments discussed subsequently is not as realistic

as one would wish. By comparison of forecasts based upon 'climatological'

and 'analyzed' sea surface temperature we may be able to clarify the

magnitude of the effect. Ideally, we would like to perform an integration

using the more realistic temperatures shown by both Bosart and the NMC

Ocean Services Group. Such an experiment will be attempted at a later

date.

Bosart presented a detailed description of the evolution of the

coastal cyclone. He shows evidence for the development of a coastal

front along which a cyclonic circulation develops. The cyclone appears

to move over land just west of Cape Hatteras at 0900 GMT 19 Feb 79. At

1200 GMT 19 Feb 79, the storm is located just east of the Delmarva penin-

sula with central pressure less than 1008 mbs.

In subsequent discussion, we will emphasize the 24 hr forecast

position of the storm produced in the several experiments. We have

examined neither the six-hourly storm positions, nor the detailed structure

of the forecasts. If we are able to repeat the experiment with corrected

sea surface temperature fields, a detailed diagnosis of the forecast

fields may be warranted.

Operational Model Capability

In this section we discuss the forecasts produced by the operational

version of the LFM used at the time the storm occurred and the forecast

produced by the presently operational version of the LFM model. The

same initial analysis fields were used in both forecasts. The presently

operational version of the LFM uses a coarser grid mesh (190.5 km @

60°N) than the originally operational version (127 km @ 60°N), but it

employs more accurate numerical approximations. The presently operational

LFM also employs improved formulations of convection and sea-air interactions.

The 12 hourly precipitation and mean sea-level pressure forecasts

are shown in figure 5. The map on the left in each panel is obtained

from the presently operational version of the LFM, while that on the

right is the forecast from the LFM which was operational at the time of

the storm occurrence.

Comparison of these forecasts with each other and with Bosart's

analysis of the storm shows that the presently operational version of

the LFM produces a forecast that is no better than the forecasts made

back in February of 1979.

To clarify the possible impact of the poor sea surface temperature

analysis available to the model in 1979, we have made an experimental

forecast using climatological sea surface temperatures which appear to

have been somewhat more accurate. We also introduced into this experiment

the new convection parameterization. The results through 36 hours are

shown in figure 6.

We notice no improvement in the forecast. The results in this run

appear somewhat more like those obtained with the presently operational

LFM, even though the result came from a model with higher horizontal

PRECIP./700

r Q13 S A.

,, 1'~ \ , - . . ) - :5

CST SFC/1000 500 T~HICK~J SVLID OO N19 FEB 1979 '9~

11 -iJ N' 1 1 - I Z - N

) I.(

--- ,,,i/g.4 va \

/- f S < , - .. t_; ' " ] " : >

,~ +~~~~~

?f~~~~J )\~~~' +-~.,-../ : ; Lo . . .. ..QP 24

.. / .I /'

M..24HR FCST. PRECI../700 ERT VEL VAL 19 F:.--B 1979 L1M9

. ,~1 -....,r~ .....1 ...... '/~~~~~~~~~~~~~~~~,---._ ' /"L:~ / t,'~iN0.~~~~ / -'--- . I-.' II . . . . .

-/ ,3 I.~-4- N, ' / -. .. 'I"1 N ./-~~~~~~~~~~~~~ //- '" /,) . ~ - ' ,O q ~ . . - z-~ .[~~~~~~~~~~~~~~~ ~ ~ ~. / If7 '~ ~ ~ ~~~~~~ ~ 'I_ .Lr~. ..,

' _7 / ' ~- ) '1-U , . Ii'',,o, ~ \ } ,...-'-' ~ ', ,' ~N./ *,. . , ' 'C .t . -- , -'/x- '. io, _ t / *ty.; ,,:- ,@~....I ~ ~ ~ ~ ~ : ..-- -:--".,~ ,

. ~ ~~~ N. \- +~ '. .':-: N'-'--- .. ~ ~...

H .. 2qR FDS T PRECIP./700 VERT VEL VALID 12Z-HION 19' FE'B 1979 LI19...

,I- �:( g- (�-

%:' I s 3

I,

I -

1

'

hf

-. �01

- '2N

A + �..

-' '� ,**

�,n. * / I agzza A-

- � *O���*)2o I � �. ( g-- - - \

* - 1, , '.4- * Tg?

1* �-'

* 36HR FCST PRECIP./700 ERT VEL VALID OOZ TUE 20' FEB

\ \_Ip l_? ,, '4 ......- ~:<·i '~ < "I')/~~- " "" ' -

j

I ,t

_ r_ ...... r\' ,. ' 't--' X~- ' ......-2 .. . . .. t ,' .- ;.

+ J s 0 t . _ I

......... '~ _.-%''~ ;''S-s '' 1a _ J_. ?-

'i- ... ~' ~-'--"C:IN: _ i ,

+

'!\P 36

) -, f\ -,- >,~ ~ ~~~~ " , F

s _ t n, v .1 Qp 36 0 ' L , -- /A - -_ _ - .; \ T 2....

L VID OOZ T - F ' LF-0- . '/ N -.

l l S ! + i / /

+ N ~ ~ ~Vt / \ A6' )P~-RF

L VALID OOZ TUE 20 FEB 1979 LFM09 - .

F.' s

,Fk -� , , F--

,0~~ ~d~ %/' C : Z 0;-:; : .Q ~ ~' 48 -/ -c7

.- Q

'BHR FCST TREUP/7020r VLE I*~k~ \/V.N.48 CS fCP1W TVS AI 2 w n

A<

; :: . ' I

SFC/1000-500

�-- ( �A

V / : 4/ i t' I

,~~~~~MT

/~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/ I --- , .-, v -:

7t', 'k-) J.._ ,' I/~,"~;' ~-..->,,.. :;/, .-.. _. 'I- ' ', ~ . 1' '. . '~.-_. ,..----¥' ,;c. ...:'- "'

-. '2Z 1 · ' -,

~~~~~~'.--2'- ',- ....

24HR FCST SCIO 50THCNS.VLD1ZMN9 81979 L

FeS "~.x,

tF l~ ~-"-'--- ..-. ' --'·. ..

7- I f

r-c,- 7

'x~~~~~~~~~~~~~~~~~~~~ -~~~~~/'"

,'

I . ,, - , . I.- .c '..'J,,.-

- ' '~ ~ _t&~~~~~9 '

-.~~~~~~~~~~~~~ ,,~ ~ ~ ~ ~ ~ ~ ~~~~2 ,,._, ' :,".':*_--~ _:_,~.~_,/..i",o ~ ~ ~ ~ ~ -oj..?~ '',-' ",'~-L.-~ p .*~ ~o *~jJ ; 'A"

,- ..~.~.~ ~_~~**

36' FS RCP/0 R E V~ 0 U~ E 99 LM

I /' ' ' ~:~ ~ ""~~~,. -: -

Hs e~~~~~~

'Fuz..

36HR FCS SFC/1000-500 I S .. %s36HR~~~~~~~~~~~~~.~--. FC/F/00SOTICNS AI O UE2FB99lto

V-,G- 76i3

resolution. This result suggests that the forecast is not very sensitive-

to the sea-surface temperature, convection formulation or to horizontal

resolution.

Ten Layer Version of the LFM

Newell (1981) presented results obtained with a ten layer version

of the LFM II model. Those experiments were conducted to evaluate the

impact of air-sea interactions on the model forecasts. Very recently,

Collins et al. (1981) presented their results of an intercomparison of

several regional forecast models, including the ten layer version of the

LFM II. Except for some problems with warm season convective precipitation,

the ten layer LFM II performed as well or better than all other models

tested.

This ten layer version of the LFM has tropospheric vertical resolution

of about 120 mbs and stratospheric resolution of about 70 mbs. It also

includes a 50 mb surface boundary layer. The horizontal resolution is

127 km at 60°N latitude on the polar stereographic map. The model

incorporates all the physical processes contained in the presently operational

LFM, including a bulk aerodynamic estimate of evaporation from the sea.

Figure 7 shows the 24 and 36 hr forecasts of 12-hourly precipitation

and mean sea level pressure produced by the ten-layer model. The predicted

position of the storm at 1200 GMT 19 Feb. 79 agrees with Bosart's analysis

of the storm's position at 0900 GMT 19 Feb 79, although the forecast

storm is to the east of Bosart's position and is about 3 mb deeper. The

predicted precipitation (isoplethed at intervals of 1/2 inch) agrees

quite well with Bosart's analysis.

It seems clear that the increased vertical resolution of the model

permitted the achievement of a much more accurate forecast of this storm.

Conclusions

From the results presented here, it seems evident that for certain

types of storms greater vertical resolution is required in NMC's operational

regional forecast models.

We could show no direct evidence that more accurate sea surface

temperature analyses are necessary, but since the impact of air-sea

interactions on model forecasts was conclusively shown by Newell (1981),

it is obvious that reasonably accurate sea surface and atmospheric temperature

analysis are essential for predicting east-coastal cyclogenesis. We

ought to repeat this forecast using more accurate sea surface temperatures.

The details of the coastal frontogenesis and the impact of convection

are difficult to document in forecasts produced with models developed

for operational use. It seems that additional progress in operational

model development will require the construction of versions of the

operational model that lend themselves to detailed diagnosis. To do

this effectively NMC will need to significantly enhance its computer

graphics capability for use in research and development.

At NMC we are planning continued development of high resolution

models for operational use; and in addition we are emphasizing the develop-

ment of improved objective-analysis systems. The implementation of

these new methods is dependent upon NOAA's acquisition of an augmented

computational facility. It is our expectation that a President's Day

storm in 1983, should it occur, will be predicted with a precision far

surpassing the result achieved in 1979.

References

Bosart, L. F., 1981: The President's Day Snowstorm of 18-19 February

1979: A Subsynoptic-Scale Event. Monthly Weather Review 109:7,

pp. 1542-1566.

Collins, W., et al., 1981: Regional Model Intercomparison Unpublished

manuscript (70 pp and figures). Development Division, National

Meteorological Center, NWS, NOAA, Washington, DC.

Gerrity, J. P., 1978: The LFM Model - 1976: A Documentation NOAA Tech.

Memo NWS NMC 60, 68 pp., National Weather Service, NOAA, Dept. of

Commerce, Washington, DC

Newell, J. E., 1981: Experiments on the Parameterization of the Flux of

Sensible Heat and Moisture from the Sea Surface into the LFM Boun-

dary Layer. Office Note 237, National Meteorological Center, NWS,

NOAA, Washington DC

Newell, J. E. and D. G. Deaven, 1981: The LFM-II Model - 1980.

NOAA Tech. Memo. NWS NMC 66, 20 pp., Nat. Wea. Service, NOAA, Dept.

of Commerce, Washington, DC