Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 282103

Area Forecast Discussion
National Weather Service Riverton WY
303 PM MDT TUE JUN 28 2016

.SHORT TERM...Tonight through Friday

Convection across the extreme east are trying to intensify in the
better moisture/instability, but are marginal at best right now.
Had a wind gust of 64 mph at Hiland which prompted the current
severe thunderstorm warning for Natrona County. However overall
storm do not look to be impressive, but large temp/dewpt spreads
could cause isolated dry microburst. The main severe weather
threat should end around 6 pm as the energy begins to shift away
from the area. There will be still isolated thunderstorms in the
area after 6 pm...but the intensity will be less...and much of
the activity should be gone by 9 pm. Will keep severe wording for
large hail/damaging winds across Johnson and extreme eastern
Natrona County thru 6 pm...but elsewhere the main hazard will be
very gusty winds with an inverted V- soundings in place.

On Wednesday and Thursday, the strong upper level ridge over the
Four Corners Region will gradually weaken with the northern
periphery of the monsoonal moisture overspreading the forecast area.
At the same time, a strong shortwave trough pushing south/southeast
out of Manitoba into the Upper Midwest will send a backdoor cold
front into the area Wednesday night/Thursday reinforcing a weak
frontal boundary already in place east of the Divide. Precipitable
water values that have been between 0.25 and 0.50 Monday and Tuesday
will increase to between 0.50 and 0.75 inches Wednesday and Thursday
with slightly better values east of the Divide Thursday as a more
substantial moist east/southeast flow develops in wake of the
backdoor cold front. Isolated to locally scattered convection is
expected both days across much if not all of the area with an
emphasis east of the Divide. The convection will linger well into
the night with the monsoonal moisture pushing into the area.

Much of the same on Friday...except for slightly warmer temperatures
and perhaps a bit less convection as the low level easterly flow is
not as strong. However still isolated to locally scattered.

.LONG TERM...Friday night Through Tuesday

Models similar with the overall evolution of the synoptic pattern
during the extended period. However, there are significant
differences from yesterday`s model runs compared to today`s
regarding the shortwave for Independence Day. Relatively flat,
zonal flow expected Saturday and Sunday ahead of developing upper
low in the Pacific Northwest. It will be difficult to time
embedded disturbances in the flow, but 700-500mb layer moisture
shows that Saturday may be the best day for more widespread weak
convection during the 3-day holiday weekend. Convection will be
diurnally and terrain driven. It appears warmer and drier for
Sunday, with convection again mainly confined to the higher terrain.
It still looks warm, windy, and dry for Independence Day, but both
the ECMWF and GFS are not nearly as far south with the upper low
late Monday. Instead of swinging through Montana, it now appears
that the low will remain over Alberta and Saskatchewan. ECMWF has
even slowed the forward progression by about 24 hours. So, expect
the flow to back to the southwest with increasing wind speeds
Independence Day but it may not be quite like what we saw last
Friday. Fire danger will certainly be up as a result of the dry
and windy conditions, coupled with temperatures 5-10F above
normal. With track of the upper low so far to our north, see
little chance of a weak front sliding south and only slightly
lower wind speeds for Tuesday. Therefore, would expect the warm,
windy, and dry trend to persist into Tuesday.



Expect conditions to remain VFR through 00Z/Thursday. The one
exception will be local MVFR with the strongest convection north and
east of a line from KCOD to KCPR through about 02Z/Wednesday and
again after 20Z/Wednesday. Shortwave now descending east-southeast
across northeast Wyoming this afternoon. Convection has fired
ahead of this feature along a line from central Johnson to
western Fremont County. Storms are moving at 30-40 mph, and
visually are not producing heavy rain. Looks as though the main
hazard will remain gusty outflow wind. Temperature-dew point spreads
still hovering around 50F. Short-range models and current
movement suggest convection will wane after 01Z-02Z/Wednesday as
shortwave tracks east away from the forecast area. Could be a few
lingering weak showers across the north half of the area through
04Z with gusty outflow wind the main hazard. Convection Wednesday
afternoon will again favor northern and eastern Wyoming to include
KCOD and KCPR. Less excited about KWRL due to distance from higher
terrain and large temperature-dew point spreads. There will be a
better chance of gusty west-southwest wind at KRKS after
20Z/Wednesday; otherwise, winds will generally be less than 12kts
at all sites.



Showers and thunderstorms will exit from west to east late this
afternoon and evening with some strong thunderstorms over Johnson
and Natrona Counties. Trend for Wednesday and Thursday will be
slightly cooler temperatures, higher RH with isolated to locally
scattered thunderstorms each day. A cold front moving from northeast
to southwest is expected to push across the region Wednesday night
and Thursday with surface winds in most places being northerly or
easterly. Thunderstorms will be mainly wet east, and more dry west
of the Divide.  Sunday into the Fourth of July looks to turn very
warm to hot, mainly dry and breezy to windy.


.RIW Watches/Warnings/Advisories...None.



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