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Area Forecast Discussion (AFD)

Issued by Cheyenne, WY (CYS)

FXUS65 KCYS 200319

Area Forecast Discussion
National Weather Service Cheyenne WY
919 PM MDT Mon Aug 19 2019

Issued at 916 PM MDT Mon Aug 19 2019

Though pretty dry right now...dewpoints are beginning to increase
in the Panhandle this evening with southeast winds. Td at Alliance
up to 66...Scottsbluff 62 and Sidney 64. Southeasterly winds
continue this evening through Tuesday morning. HRRR and SREF
hinting at low clouds and fog moving in after 09Z. Decided to add
fog to the forecast tonight through 15Z Tuesday.

UPDATE Issued at 803 PM MDT Mon Aug 19 2019

Area observations have been showing a down trend on wind speeds
and a slow uptick in humidity this evening. Went ahead and let the
Red Flag Warnings we had out...expire on time at 8 PM. Updates
have been sent.


.SHORT TERM...(This afternoon through Tuesday night) 
Issued at 230 PM MDT Mon Aug 19 2019

A upper level ridge dominated the south-central CONUS with warm 
and dry zonal flow aloft. 700mb temperatures in the mid-upper teens
Celsius and gusty downsloping westerly winds pushed the mercury 
into the 90s east of the Laramie Range. Cheyenne eclipsed its daily
record high temperature of 92 degrees in 2001 with 95 degrees. 
Visible satellite imagery revealed a scattering of cumulus clouds 
across much of the Cowboy State. The combination of warm temperatures,
gusty winds and low humidities was creating critical fire weather
conditions across portions of south-central and southeast WY this
afternoon. Dry and mild weather will prevail tonight under partly
cloudy skies. 

A cold front poised just north of the Canadian/US border is forecast
to progress southward into western NE and eastern WY plains Tuesday
afternoon, shifting winds into the east. Low level easterly upslope
flow will introduce cooler temperatures, increasing moisture and 
instability east of the Laramie Range during the afternoon and 
evening. NAM sounding profiles are progging MUCAPEs upwards of 
3000-4000 j/kg with bulk shear values of 40-50 kt. The SPC Day2 
Outlook includes much of the NE Panhandle in a Slight Risk for 
severe thunderstorms, with a Marginal Risk extending west to the 
I-25 corridor. The primary hazards will be hail (ping pong ball 
size or larger) and damaging downburst winds of 60-70 mph. With 
precipitable water values rising to 1.25 inches across the plains 
Tuesday evening, will also be concerned with locally heavy rainfall
and minor flooding. Models have been consistent with convection 
lasting into the late night hours east of the Laramie Range.

.LONG TERM...(Wednesday through Sunday night) 
Issued at 335 AM MDT Mon Aug 19 2019

Showers and thunderstorms will continue Wednesday and possibly
Thursday ahead of a slow-moving Pacific system which will push
east along the Canadian/US border through the middle of the week.
Some stronger storms are possible Wednesday afternoon, but with
the lack of decent 0-6km shear near the upper level ridge axis 
any concerns are limited at this time. Once this Pacific system
moves east, drier air will filter into southeast Wyoming and
western Nebraska for next weekend. Extended forecast then becomes
uncertain into the last week of August as some models are hinting
towards the first polar cold front of late summer moving southward
out of Canada and into the northern Great Plains. The GFS and 
Canadian both show this cold front moving across the Front Range 
and bringing much cooler temperatures. but this feature is still 
8 to 10 days out.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 524 PM MDT Mon Aug 19 2019

VFR. Wind gusts to 20 knots at Rawlins and Laramie until 04Z. 
Wind gusts to 27 knots at all sites after 15Z to 19Z Tuesday.


Issued at 143 PM MDT Mon Aug 19 2019

Elevated to critical fire weather conditions will continue this 
afternoon across much of southeast Wyoming due to warm temperatures,
gusty winds and low humidities. A cold front is forecast to move 
south across the plains Tuesday and stall along the Front Range 
through Thursday. Areas along and east of the Laramie Range can 
expect cooler temperatures with scattered showers and thunderstorms
from Tuesday afternoon through Wednesday night. A few strong to 
severe thunderstorms will be possible. Areas west of the Laramie 
Range can expect mainly dry and warm conditions.