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FXUS65 KCYS 270930
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
330 AM MDT Tue Jun 27 2017

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM MDT Tue Jun 27 2017

Today will be a change from the recent dry and mild weather
pattern we have gotten used to over the past week. A shortwave
trough will track just north of our area late this afternoon as an
upper level jet noses into SE WY. Height falls aloft and upper
diffluence will serve to strengthen a sfc trough over the plains
this afternoon. Strong moisture transport already in place as
dewpoints early this morning are well into the 50s east of the
Laramie Range. Given the moist SE flow have seen some low stratus
start to form over the favored upslope locations so will need to
monitor places like the I-80 summit for fog formation.

Sfc trough will surge eastward into the NE panhandle early this
afternoon. Most CAM's are developing widely scattered storms along
this trough and then quickly moving them eastward and out of our
eastern counties mid/late afternoon. Have doubts about the coverage
of convection east of the surface trough as 700 temps warm to 14-16C
so will have to wait for strong sfc heating to overcome this cap. By
this time storms can really get going, think the best low level
moisture will be to our east. Shear profiles are favorable for
supercells so if things can get going a bit earlier, large hail and
damaging winds are a possibility. This would be more likely in our
easternmost row of counties. A second area of convection will most
likely form over the higher terrain in a deeply mixed, warm and dry
BL. This activity will be high based and looking at strong wind
profiles and inverted-V soundings which would promote gusty
downdrafts with very little in the way of measurable precipitation.
This activity will be most prevalent over our northern counties
closer to the shortwave energy aloft. It will also be a breezy to
windy day west of the Laramie Range with the deep mixing especially
early in the afternoon. Wind gusts of 40-50 mph are likely
especially in our wind prone areas with pressure falls to the north
and east.

Front will move across the area this evening with gusty west to
northwest winds persisting into the late evening hours. Wednesday
will be a slightly cooler day and with weak shortwave energy aloft
during the afternoon, expected continued chances for afternoon
convection especially in SE WY near the higher terrain.

.LONG TERM...(Wednesday night through Monday)
Issued at 330 AM MDT Tue Jun 27 2017

The afternoon convection developing along the higher terrain of SE
Wyoming Wednesday will spread east onto the high plains Wednesday
evening as the next shortwave moves east across central Wyoming.
We will keep some PoPs going across the northeastern half of the
forecast area into Thursday as that shortwave drives eastward
across the area, then we see a drop in significant rain chances
through the rest of the week as most of the stronger shortwave
energy passes our area to the northeast with weak upper ridging
building in from the southwest.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday)
Issued at 330 AM MDT Tue Jun 27 2017

IFR ceilings being observed around Cheyenne early this morning
with a solid deck of IFR ceilings moving in from the south to the
Kimball and Sidney Nebraska areas. This deck of low clouds should
spread northward to Alliance and Scottsbluff through daybreak
and will linger in the persistent strong southeasterly upslope
boundary layer flow until mid morning. Otherwise, expect VFR all
sites by afternoon, however strong southerly winds at Chadron
gusting to near 40 kts at times will continue into late morning
before weakening a bit as they will be under the axis of the
strong southerly low level jetmax (40 to 50 kts) ahead of the
approaching surface trough over eastern Wyoming. Showers and
isolated thunderstorms this morning and afternoon will be capable
of wind gusts 40 to 50 kts due to dry subcloud layer, with the
fist round of gusty showers moving through the Rawlins area early
this morning.

&&

.FIRE WEATHER...
Issued at 330 AM MDT Tue Jun 27 2017

Dry and windy conditions will develop especially west of I-25
this afternoon. A few high based thunderstorms may develop but not
much in the way of wetting precipitation expected. Elevated
conditions will likely occur with RH values in the 10-15 percent
range and west winds gusting between 40 and 45 mph at times. While
fuel status remains green, there is at least some marginal
concerns this afternoon. Breezy conditions look to develop each
afternoon Wed and Thu but with cooler temps and RH values maybe
not quite a low as this afternoon.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...DEL
LONG TERM...Garmon
AVIATION...Garmon
FIRE WEATHER...DEL
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