utah climate update newsletter (sep 11)

8/4/2019 Utah Climate Update Newsletter (Sep 11)

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UTAH CLIMATE CENTER UTAH STATE UNIVERSITY 435-797-2190 http://climate.usurf.usu.edu/

High pressure over the four-

corners region, combined with

monsoonal flow from the Pacific,

dominated Utahs weather for the

month of August. In last months

newsletter we discussed the

mechanisms underlying the Southwest

Monsoon and its critical importanceto the region. This month its worth

spending some time on the larger-

scale atmospheric circulation pattern

that directs this moisture as it flows

into the

southwest.

A semi-

permanent

feature to the

region is the

North American

sub-tropical

ridge. This

tongue of high

pressure migrates

northward with

the onset of high

summer,

channeling the

moist monsoonal flow well into

Arizona, Utah, Colorado and New

Mexico. Just how far north this ridge

decides to venture determines to largeextent the amount and location of

convective rainfall various locations

receive. If the ridge stays south, the

monsoonal flow is cut off and

summertime rain is suppressed.

Further north, stretching toward the

Four Corners, and the monsoonal flow

is drawn deep into Utah and

Wyoming. One variation of the

North American ridge is formation is

formation of a full-fledged anticyclone

a bona fide high pressure system.

This happens when isobars close and

a fully anticyclonic (clockwise) flow

develops.

This is precisely what developedthis past month over the Four Corners

region. Combined with a strong

monsoonal flow, the pattern produces

a readily visible signature in the

regions afternoon

satellite and radar

imagesa ring of

convection, roughly

centered over the

Four Corners and

covering large

portions of

Arizona, Utah,

Wyoming,

Colorado and New

Mexico. Also

evident in the

signature is a

notable absence of

convective activity near the center of

the High. Its likely this consistent

pattern arises from the competing

influences of the tendency of warmsurface air to rise vs. the tendency of

air within a high pressure system to

sink. Further from the center of the

high, the thermally driven convection

wins. But underneath the highest

pressure, subsidence dominates.

September Feature

Four-Corners High

THIS MONTH...

9.1SEPTEMBER FEATURE

Four-Corners High

9.2SEPTEMBER FEATURE

First Freeze

9.3AUGUST REVIEW

A look back at Aug precipitation

precipitation

temperatures

Vegetation Drought

Response Index

9.4CLIMATE NOTES

National and global notes ofinterest

Record low Arctic Ice

Texas Drought

9.5BACK PAGE

Ongoing at the Utah Climate

Center Arid China

Africa Research

A New Grant

UTAH CLIMATE UPDATE, ISSUE 35 SEPTEMBER, 2011

Utah Climate Update

Figure 1. Circulation around high pressure isanticyclonic, or clockwise.


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Just when can you expect that first freeze this year?

Or any year? From finally killing off the tomatoes

and the grasshoppers to reminding us its time to get a

new windshield scraper for the

coming winter, first freeze dates

defined as the first day in

which the daily minimum

temperature drops below 32degrees F are of little more

than casual interest to most of us.

But for the agricultural

community first (and last) freeze dates of the season

can have a critical impact on operational decisions.

Consequently, at the request of the Utah Agricultural

Experiment Station (UAES), housed at Utah State

University, the Utah Climate Center recently

undertook development of a new method for

location-specific first-freeze date

forecasting. Taking a climatological,

rather than meteorological, approach,

the effort is underway.

In this first effort, a pilot project, theforecasts have been made for six

location in Cache County. The UAES

owns and operates several research

farms throughout Cache Valley. With the wet

weather this spring, crops are about 30 days behind

normal in the valley. Decisions need to be made

Figure 2. Drawing on Pacific monsoonal moisture, the Four-Corners High produces a ring of afternoon thunderstorms across Arizona, Utah, Wyoming, Coloradoand New Mexico. Also evident in this signature is suppressed convection at the center of the high pressure system, where sinking air (subsidence) is strongest.


HighPressure

low-moisture

level

September Feature

First Freeze?


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concerning when to harvest cornspecifically,

whether to chop it for silage or to hold out for a high

moisture corn harvest.

UCCs approach to the question involves analysis of

historical data, combined with the National Oceanic

and Atmospheric Administrations (NOAA) Climate

Forecast system, or CFS a climate model using

gridded data. The UAES

locations are tailor

made for the pilot

study, in that each

location is close

to

meteorological

observing

stations

(specifically, the

data comes

from nearby

COOP

stations).

Empirical analysis of

the historical data,

going back 30 years to

1981, shows that, atsome locations, the first

day of fall freeze (and

last spring freeze) is a

function of monthly

surface temperature.

That is, there appears

to be a significant

correlation between

Septembers mean daily

minimum temperaturesand when the first freeze occurs. Using this

relationship, UCCs Dr. Simon Wang built a model

(specifically, a regression model) relating historical

freeze dates and September mean temperatures for

various stations over a 30-year timespan. He then

constructed a regression function (a mathematical

relation) between surface temperatures of the station

and of the operational forecast model (NOAAs CFS).

To produce the forecast, the predicted September

mean temperature over northern Utah is "plugged in

to" to the regression functions of one station. The

output, then, is the predicted date of first fall freeze

for that particular station. The results are depicted in

Fig. 3 below. Broadly, they tell

us most locations in

Cache Valley can

expect a first freeze

this year in the first

week of October.

This is tied to the fact

that the CFS

September

temperature

forecast

remains slightly

warmer than normal,

according to NOAA.

Further, there is a

67% probability that

the first freeze will

occur within 5 days ofthe highest

probability date (the

dates shown in the

figure), and a 95%

probability that it will

occur within 9 days of

the given date. (In

statistical lingo, thats

a 1-sigma uncertainty

of 5 days and a 2-sigma uncertainty of 9 days.)

Eventually the results will be translated togridded data for the state and the region

assuming, that is, the method proves accurate.


October 6( 5 days) October 5

( 5 days)

October 2( 5 days)

October 4( 5 days)

October 3( 5 days)

October 1( 5 days)

Figure 3. First freeze predictions for various locations around Cache Valley. This is a trial run,with planned expansion to the entire state.


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30 days (August) 60 days 90 days 180 days

0 5 10 25 50 75 90 100 110 125 150 200 300 400 600

Percent of 30-year mean

Precipitation

Looking back at August

Precipitation across Utah in August was down considerably, compared to May and June. Climatologically, most of the state is

now well below normal for the month. Still, owing to the wet spring, parts of of the state are closer to normal at the 3-month

and 6-month timeframes.

30 days (August) 90 days 365 days

Departure from 30-year mean (F)

-10 -8 -6 -4 -2 0 2 4 6 8 10

-5 -4 -3 -2 -1 0 1 2 3 4 5

30 days

90 days

365 days

-10 -8 -6 -4 -2 0 2 4 6 8 10

August temperatures across Utah were substantially above normal in contrast to July, which saw essentially seasonal

temperatures. High pressure centered over the Four Corners brought sinking and warming air, with Utahs southeast and

southwest bearing the brunt of the warmth. Still, the imprint of a cool spring and cold winter remain at the 3-month and 12-

month timescales.

Temperature



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Vegetation Drought Response Index

Looking back at August

The Veg DRI is a hybrid drought index intended to

help better assess drought from the standpoint of

agriculture. This product combines climate-based drought

index data (e.g., the Palmer Drought Severity Index and the

Standardized Precipitation Index); vegetation conditions

(based on satellite observations); and biophysical

parameters (e.g., land cover, soil type, ecology, elevation).

Spatial resolution of the Veg DRI is about 1 km, and is

updated at 2-week intervals during the growing seasons.

The National Drought Mitigation Center produces VegDRI in collaboration with the US Geological Survey's (USGS) Center for Earth Resources

Observation and Science (EROS), and the High Plains Regional Climate Center (HPRCC), with sponsorship from the US Department of Agriculture's

(USDA) Risk Management Agency (RMA).

Source:NationalDrought Mitigation Center

August 22, 2011


Extreme Drought

Severe Drought

Moderate Drought

Pre-Drought

Near Normal

Unusually Moist

Very Moist

Extremely Moist

Out of Season

Water

Vegetation Condition


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Global

Climate Notes

Polar ice cap From the National Snow and Ice DataCenter (NSIDC), Arctic sea ice has nearly tied the record

minimum extent in area for the month of August. And

from the University of Washingtons PIOMAS group,Arctic sea ice volume is at a record low.

Texas Drought At the end of July, the U.S. state of

Texas had experienced its driest AugustJuly (12-

month) period on record. As of August 23rd, close to

100 percent of the state was experiencing some level of

drought and 78 percent fell into the exceptional category,

the highest drought category as determined by the U.S.

Drought Monitor. The agriculture industry has been

exceptionally hard hit. According to a media report

updated on August 17th, from November 2010 to August

1st, 2011, Texas suffered an estimated $5.2 billion U.S.

dollars in crop and livestock losses, surpassing the previous

annual record loss of $4.1 billion U.S. dollars in 2006. The

losses this year are expected to grow as the drought shows

no signs of abating. Additionally, wildfire danger was great

across the arid region. A 30-acre blaze in the central Texas

town of Leander destroyed 15 homes. One particularly

vivid graphic, created by Texas state climatologist John

Nielsen-Gammon, illustrates the historical relationship

between temperature and rainfall. Shown below, we see

(not surprisingly) that warmer summers are drier. But

striking in the data is just how far 2011 resides outside the

historical envelope.

National


Drought Intensity

Abnormally Dry Moderate Severe Extreme Exceptional Jun-Aug Total Rainfall (inches)

2011

Texas Summers

Jun-AugAve.

Temperature(F)

199819801934

78

88

83

2 6 8 14

2010the normal

definitely

notnormal

Arctic Sea Ice VolumeArctic Sea Ice Extent


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Come September, its

time to think of Autumn. The

dropping angle of the

midday sun and the

first crisp mornings

since early July. Here

in Cache Valley, we

even dipped into the 40s this morning

a welcome relief from the heat of last

week. And September means the start of

another semester here on the USU

campus. Taking a deep breath

Arid China...Completing a hat trick of Asian travel

this summer (including Mongolia and

Nepal), I attended a conference in

Yangling, Shaanxi, China this past month,

regarding the efficient use of agricultural

water in arid regions. This visit

complements a previous visit to China and

research we here at the UCC have

undertaken in the region.

Africa Research ...

Just to make sure we touch as many

continents as possible in this monthsnewsletter, Id like to announce the

publication of UCCs most recent piece of

research, Observed change in Sahel rainfall,

circulations, African easterly waves, and Atlantic

hurricanes since 1979, in press in the

International Journal of Geophysics. In

this paper we examine the recent increase

in the Sahel rainfall. The rainfall that has

been observed to be increasing over the

Sahel is accounted for by enhancements in

both the jet stream. This increase signals

an increased potential for the occurrence

of flash floods along the northern Sahel. In

addition, the analysis suggests that the

change reveals a link to increased activity

of intense hurricanes in the NorthAtlantic.

A new grant

Researchers here at the Utah Climate

Center have recently been awarded a grant

from the Bureau of Reclamation to study

climate modeling in the Colorado River

Basin. Specifically, the study is entitled

Effective Assessments for Climate Uncertainties in

Dynamical Downscaling over the Colorado

Regions. (Say that three times in a row!)

Follow us on Twitter ...

Between newsletters, be sure to follow

us on Twitter (utclimatecenter).

From the Director

UTAH CLIMATE

CENTERThe Utah Climate Center is

located on the Utah State

University campus in Logan, UT.

Utah Climate CenterUtah State University4825 Old Main HillLogan, UT 84322-4825Telephone: 435-797-2190

Staff

Staffdr. robert gilliesdirector

dr. randy martinassociate director

marty boothstaff meteorologist

jobie carlisletechnician

dr. shih-yu (simon) wangassistant professor, PSC

research associate, UCCdr. robert davieseducation / research associate

Martin Schroederstaff meteorologist

Photo Credits

banner: Autumn in Zion National

Park, courtesy of David Bostock

(www.dbphotography.net)

front page: Dixie National Forest in

Autumn, courtesy of David C. Schultz

(www.westlight.net)

back page: Autumn in Zion NationalPark, courtesy of David Bostock

(www.dbphotography.net))

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