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fxus65 kbou 191547 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
947 am MDT Wed Jun 19 2019

issued at 945 am MDT Wed Jun 19 2019

Adjusted sky grids to reflect the clearing from west to east, as
well as refined the pop grids to reflect the consensus of the
high-resolution models of a better chance to see the first storms
of the day popping over northern Weld County then pushing east,
as well as adding a slight chance of showers/storms over southern
Lincoln County later this afternoon. No other adjustments needed
at this time.


Short term...(today and tonight)
issued at 301 am MDT Wed Jun 19 2019

Another wave of showers and thunderstorms is slipping across the
Wyoming border at this time. Will keep the mention of this in the
grids until around 12z, then these showers/thunderstorms are
expected to dissipate as the short wave exits the cwa. Patchy fog
will persist as well until around 15z mainly north of Denver and
east of I-25. For today, the mid and upper levels will becoming
drier and more subsident by this afternoon. Temperatures today
will climb back to near normal. Thunderstorm coverage will be
isolated across most of the forecast area. Fairly healthy convective available potential energy
still exist however over the far northeast plains. Storm Prediction Center still
keeps a marginal risk of severe thunderstorms along the
Nebraska/Kansas border this afternoon, with a better chance of
thunderstorms east of Sterling and Akron line. Convective available potential energy still around
1500-1800 j/kg there this afternoon with the stronger storms
capable of producing moderate to heavy rainfall, hail up to nickel
size and wind gusts in the 50-60 mph range. A stronger
northwesterly flow aloft will negate any flooding threat. In the
mountains, it will be windy especially above timberline. Late
tonight, nam12 spatial cross-sections show some mountain wave
amplification so stronger winds expected to occur in the Front
Range mountains and higher foothills of Boulder and Larimer
counties. Gusts around 50 mph range may develop in those areas
after 06z.

Long term...(thursday through tuesday)
issued at 301 am MDT Wed Jun 19 2019

On Thursday, a large upper level low will be over the northern
rockies with several short wave troughs rotating around it. Over
Colorado, westerly flow aloft will prevail. At the surface, a low
pressure trough will be east of the foothills. West of the trough,
gusty westerly downslope winds will prevail. East of the surface
trough, southerly flow will transport moisture northward. Surface
based cape east of the trough will be up to 500-700 j/kg, so a few
strong storms will be possible. Precipitable water values are
expected to range from a half inch over the higher terrain to
three- quarters of an inch across the plains, somewhat higher than
expected given the westerly flow. Temperatures will warm to near
normal with highs in the 80s across northeast Colorado. A jet at
base of the low is expected to provide lift over northern parts of
the area. This is where the most showers and storms are expected
to be.

The main upper level low tracks east across Montana Thursday
night and Friday. One piece of energy rotates south across the
Great Basin Friday and strengthens into a deep trough or closed
low over Nevada. Flow aloft turns southwesterly across Colorado.
Models show a cold front pushing south through eastern Colorado
sometime Friday. The timing is still unclear. Upslope flow behind
the front and lift from the jet, combined with precipitable water
values nearing an inch along the Front Range should result in
numerous showers and thunderstorms. May be a marginal severe
threat as well Friday. Biggest challenge for this...will it be
unstable enough for severe storms. Plenty of shear will prevail
with the strong flow aloft.

Models still trying to resolve what happens to the upper level
low/trough over the Great Basin. There is a good amount of
uncertainty on the strength and timing of this system as it tracks
east across the central rockies. On Saturday, there will be lift
from the jet and approaching upper level low/trough. Good moisture
will remain in place with precipitable water values near an inch
across northeast Colorado. A cooler airmass and cloudy skies is
expected to result in a chilly day. Highs may struggle to reach
the 70s. If there is enough clearing for temperatures to climb
into the 70s, there should be enough instability for a chance of
severe thunderstorms.

Another thing to watch is the cold air over the mountains with
this system. There is enough cold air to drop snow levels below
10,000 feet mean sea level Saturday night on the European model (ecmwf). The NAM is quicker
with the snow levels falling below 10,000 feet mean sea level by Friday
night. Most models indicate the potential for snow over the north
Central Mountain this weekend. If the cold air arrives sooner, a
good amount of snow could fall above 10,000 feet. At this time,
best precipitation is expected to occur before the cold air

Sunday's forecast is still unclear. If the low/trough is moving
over Colorado or still to the west, would expected another round
of numerous showers and thunderstorms. If the low/trough is east
of the area, subsidence behind it should limit convection to
scattered at most. Either scenario should produce another cool day
with highs in the 70s.

For Monday and Tuesday, an upper level ridge starts to build over
the southern and central rockies. This will start a warming trend
with highs reaching the 80s by Tuesday. Models indicate moisture
will decrease, but enough should be around for at least isolated


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 945 am MDT Wed Jun 19 2019

Generally expected VFR conditions over the next 24 hrs. Drainage
winds are beginning to transition to west/northwesterly late this
morning and afternoon with speeds in the 8-12 kt range. Only
isolated thunderstorm coverage today mainly near the higher
terrain and not expected to impact the terminals at this time.
Winds will return to drainage overnight, with southeast-east winds
tomorrow as a Denver cyclone develops due to a surface low forming
over the southern foothills.


Bou watches/warnings/advisories...


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