Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Cheyenne Wyoming
1129 PM MDT sun Jul 5 2015

issued at 832 PM MDT sun Jul 5 2015

The threat for severe thunderstorms continues to diminish this
evening with the loss of diurnal instability and stronger deep
layer vertical shear shifting north and east of the County Warning Area. Precipitation
has become mostly stratiform over the northern Panhandle...and
lingering convective cells over Cheyenne County have not shown
many signs of strengthening over the last hour. Per coordination
with Storm Prediction Center...we went ahead and cancelled Severe Thunderstorm Watch 391 as
any remaining threat should be very isolated. Flooding rains were
our main problem through the late afternoon/evening with a tropical type
air mass in place...and tall/skinny convective available potential energy contributing to rather
efficient warm rain processes. 3-6 inches of rain fell in parts of
Laramie and Scotts Bluff counties...resulting in several washed
out roads. Flash flood statements are ongoing at this time.

Not many changes required to the inherited forecast. We transitioned
to moderate stratiform rain with embedded thunder for northern
portions of the Panhandle through 06z...and increased probability of precipitation into
the 90-100 percent range. We ended all mention of thunderstorms after 06z
as BUFKIT soundings show very little cape. Shower activity will
likely persist through the night as a midlevel shortwave tracks
across southeast Wyo. Trended temperatures up a few degrees as
well given the moist air mass in place. Cannot rule out some fog
later on...but think winds will stay strong enough to keep the
llvls mixed.


Short term...(this evening through Tuesday night)
issued at 436 PM MDT sun Jul 5 2015

Convection has really increased through the early afternoon over
Albany/Laramie counties and portions of the southern Panhandle.
This development is occurring in advance of a weak shortwave located
over western Colorado/Wyoming. The storms over Laramie County have
been heavy rain producers with a few locations showing radar derived
amounts of one to three inches. Plentiful monsoonal moisture is
moving northeastward into the County Warning Area with precipitable water values above 1.25 inches
across the plains. It appears that the rain is becoming more
stratiform though over southeast Wyoming behind the cold front which
should reduce the heavy rain/flash flood threat through the
remainder of the evening. The potential exists for strong to severe
storms to develop over mainly the far Panhandle through this
evening. Storm Prediction Center mesoanalysis shows good instability (mlcapes of 2000-
2500 j/kg) in northern Sioux and Dawes counties with bulk shear of
30 kts. There is less instability to the south along Interstate 80.
A Severe Thunderstorm Watch is in effect until 11 PM for zones along
the eastern County Warning Area border in the Panhandle. Shortwave trough will pass
eastward into western Nebraska by later tonight with the front
passing over the entire County Warning Area. Will keep 50-70 percent probability of precipitation going
through much of the night...but again the rain should be more
stratiform in nature.

Much cooler on Monday in the Post frontal airmass. Scattered
showers could continue into middle morning across southeast Wyoming before
tapering off. Instability will be much less than previous days with
the best chance of thunder confined to areas along and west of the
Laramie range. Convection becomes more widespread once again on
Tuesday especially over southeast Wyoming. Cape does increase to
around 1000 j/kg along the Laramie range by the afternoon but drops off
quickly across the plains. Get some warming on Tuesday...however temperatures
will still be about 10 degrees below normal.

Long term...(wednesday through sunday)
issued at 436 PM MDT sun Jul 5 2015

Unsettled and warmer conditions will continue through the end of
the week as moist southwest flow remains over the forecast area.
Temperatures will warm from the 60s and 70s on Wednesday back into
the upper 70s to low 90s from west to east by Friday. A few pieces
of energy will move overhead on Wednesday...and with plentiful
moisture in place through the atmospheric column combining will
decent low level upslope flow...should see a good chance for showers
and thunderstorms through the day. Deep layer shear continues to
look favorable for a few stronger storms on Wednesday
afternoon/evening so will keep mention for that possibility in the
forecast. Thursday will be quite similar...however increasing
temperatures aloft will diminish coverage for showers and
thunderstorms a bit with the best chance expected over the
mountains. Chances for strong storms will be less as well. Models
are consistent with showing the upper low over California
becoming an open wave as it moves northeast across the Great
Basin. GFS continues to be the wetter solution vs the European model (ecmwf) on
Friday...but both models show afternoon convection developing in
the mountains. The wetter GFS carries the convection east in the
evening while the drier European model (ecmwf) keeps the eastern zones dry. Will
keep slight chance probability of precipitation in for Friday evening until models become
more consistent. For Saturday...both models build a strong upper
level high pressure center into the Southern Plains...with the
European model (ecmwf) building that ridge up into The Rockies as well. The GFS is
starting to trend that way...but still sweeps a bit more midlevel
energy across our area in the evening. Maintained a slight chance
for T-storms over the mountains to account for model
differences...but left remaining areas dry.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1126 PM MDT sun Jul 5 2015

Wyoming tafs...IFR developing the rest of the night in fog and
low clouds with mountains obscured. Becoming VFR in the morning
with scattered afternoon showers producing localized MVFR...then
IFR developing Monday evening in fog and low clouds.

Nebraska tafs...widespread IFR developing the rest of the night
in fog and low clouds...then becoming VFR with scattered afternoon
showers producing localized MVFR...and VFR Monday evening.


Fire weather...
issued at 436 PM MDT sun Jul 5 2015

No fire weather concerns through the middle of next week.
Widespread wetting rains will occur through tonight over much of the
region. A cold front will bring much cooler temperatures on Monday.
Minimum afternoon humidity values will generally be above 40
percent through Wednesday. There will be a chance of afternoon and
evening showers and thunderstorms each day through the middle of the
next week.


Cys watches/warnings/advisories...


short term...zf
long term...rjm
fire weather...zf

National Weather Service Glossary of Abbreviations