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afdcys

Area forecast discussion
National Weather Service Cheyenne Wyoming
543 am MDT Wed Jun 28 2017

Short term...(today through Thursday night)
issued at 252 am MDT Wed Jun 28 2017

Area will remain under the influence of an upper trough over
Alberta through Thursday. Weak shortwave energy will track over
our northern counties this afternoon as a 90kt upper jet noses
into northern Colorado. At the surface, a weak front will remain nearly
stationary or slowly wash out just to our south. This will set the
stage for more afternoon convection today. Model forecast
soundings once again indicate a deeply mixed boundary layer topped
by weak instability with MUCAPE on the order of 500 to 1000 j/kg.
With great evaporative cooling potential, think strong and gusty
downdrafts are once again a possibility with just about any
convection this afternoon. Most activity will be concentrated over
our northern counties where the best low level convergence and
proximity to forcing aloft are located with another area of
development along and just north of the frontal boundary over NE
Colorado. Forcing both at the surface and aloft not as strong as
yesterday but still would not be surprised to see a few severe
wind reports from the activity this afternoon.

Models show a weak front passing across the area from the northwest tonight
and with some elevated cape still present, maintained some pop even
into the night time hours.

A stronger shortwave and its attendant cold front will move across
the area on Thursday. Steepening lapse rates underneath cool air
aloft will promote continued chances for shower and thunderstorm
activity but think the wind threat will be a bit lower due to cooler
temps and less of a T/TD spread in the bl. Some hail will be
possible with the stronger storms as freezing levels lower and
mid/upper tropospheric flow remains strong. Cooler and more stable
air will filter into the area behind the front on Thursday night.

Long term...(friday through wednesday)...
issued at 252 am MDT Wed Jun 28 2017

Warming and generally dry conditions can be expected through the
period as swift northwest flow gives way to building heights beneath
a strengthening Four Corners high. 700 mb temperatures of around 3c on
Friday are progd to warm into the 15-18c range by the middle of next
week. Forecasted temperatures will reflect this trend with highs in
the 70s on Friday giving way to 80s to around 90f sun-Wed. Latest
deterministic model runs even suggest that these values are
conservative and will need to be increased with time. Expect
generally dry conditions to prevail, with the exception of isolated
shower & thunderstorm chances Sunday afternoon as a weak shortwave
moves thru during peak heating.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 543 am MDT Wed Jun 28 2017

Forecast challenges to aviation Ops today will be the timing and
coverage of afternoon and evening -shras/-tsras. Latest guidance
suggests thunderstorms to begin developing near kcys and
associated routes by 21z, shifting east into western Nebraska
terminals through 02-04z. Some indications that some re-
development will occur perhaps lingering convection into the
overnight hours. Still a fair amount of uncertainty in location
and timing, so have leaned on thunderstorms in the vicinity for now. Although convection
cant be 100% ruled out at krwl and klar, confidence is low enough
to leave out any ts mention. Although there is indication may
linger after 04z, coverage/intensity will be waning, thus
mitigating impact on terminals.

&&

Fire weather...
issued at 252 am MDT Wed Jun 28 2017

A deeply mixed boundary layer is expected once again this
afternoon. Model sounding indicate mixing heights as high as
13,000 ft. With moderate lower to mid level winds still present,
expect winds to be 20 to 25 mph with gusts to 40 mph at times
especially over Carbon County. Relative humidity values will fall as low as 10 to
15 percent west of the Laramie range so have issued a red flag
warning where fuels are ready. Dry thunderstorms also a
possibility with weak cape atop the deeply mixed bl. Strong and
erratic winds a possibility with any convection. Elevated
conditions are also possible over the south Laramie range as well
as the Rawlins area this afternoon. A cold front will move across
the area on Thursday bringing cooler temperatures and reducing the
fire weather concerns somewhat.

&&

Cys watches/warnings/advisories...
Wyoming...red flag warning from noon today to 6 PM MDT this evening for
wyz306.

NE...none.

&&

$$

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