Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 221623
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1023 AM MDT Tue May 22 2018

.UPDATE...
Issued at 1023 AM MDT Tue May 22 2018

Main change to the morning forecast package with this update is to
scale back the chance of thunderstorms on the plains through the
afternoon. Satellite imagery shows the upper level low spinning
over southwest Utah with deep meridional flow across eastern Utah
and western Colorado. The initial convection for the day has
developed over the southern slopes of the San Juans with initial
cell motions straight to the north. Models show that the today`s
convection will be driven by an upper level jet rotating around
the upper circulation and by the diffluent southerly flow over
Colorado`s western slope. Short range and mesoscale models have
been consistent with keeping the majority of today`s shower
activity west of the Continental Divide. This will leave the
plains high and dry through late in the afternoon. By evening the
shower activity will begin expanding eastward to cover the
northern Front Range foothills and adjacent plains. The HRRR also
indicates an area of showers moving over Lincoln County early in
the evening. The storms will grow stronger further to the north as
the strongest instability is indicated by SPC mesoanalysis to be
located over Wyoming. Gusty winds and hail approaching severe
limits will be the primary threat from th thunderstorms.

&&

.SHORT TERM...(Today and tonight)
Issued at 345 AM MDT Tue May 22 2018

Closed upper low is situated over southern Nevada and southern
California early this morning and will begin to weaken a bit and
lift out across Utah and western Wyoming later today and
tonight. There will be some increase in the southwest flow pattern
across Colorado and additional moisture as the low moves a bit
closer to Colorado. Best QG ascent and moisture will be over
western portions of the CWA in closer proximity to the upper low
and jet streak lifting through central and western Colorado this
afternoon.

Temperatures will be only slightly warmer today as 700mb
temperatures climb to around +11C. High resolution models have
most of the convection over the mountains this afternoon/evening
and across the Northern Front range with better pooling of
moisture and higher dewpoints. Otherwise, further east over the
plains only isolated thunderstorm coverage. Strongest storms
should be more towards the northern border areas with Wyoming as
low level easterly flow keeps low level moisture more plentiful
and CAPE values upwards of 1200j/kg. Expect mainly heavy
rain/small hail with storms but couldn`t rule out an isolated
severe storm further north towards Wyoming with marginally large
hail.

.LONG TERM...(Wednesday through Monday)
Issued at 345 AM MDT Tue May 22 2018

By Wednesday the upper low center will be over southeastern Idaho
with weak SW flow over the region. At the surface a surface low will
set up helping to pull SW winds that will help to increase
temperatures and potentially drop dewpoints on the plains. Heating
near the surface will help to create some instability and that
combined with a shortwave embedded in the upper SW flow could be
enough to spark thunderstorms over the mountains and portions of
adjacent plains. Models are currently showing the best CAPE near the
northern Wyoming border with 1000 to 1500 j/kg and 45 to 50 kts of
bulk shear. This could be enough to spark a few severe cells by
Wednesday afternoon. Outside of this area storms could possibly only
produce virga or gusty winds do to a dry low level or not develop
much at all because of warming aloft. Will keep slight chance to
chance pops in place.

For Thursday upper ridging will increase behind the shortwave as
well as QG subsidence. Conditions will dry out with temperatures
approaching the mid 80s. CAPE is weak with dry low levels so any
convection that could form would most likely result in high-based
storms with gusty winds. Will keep a slight chance on the far
eastern plains as there is decent shear and the warming layer seems
pretty weak so there is a possibly that some storms, if formed could
hold together.

For Friday into the weekend upper level ridging will increase as the
closed low makes its way towards the CA coastline. This will bring
stable conditions and temperatures approaching the 90 degree mark.

The low system will be the next major weather maker for the region.
Timing is still hard to pin down but models have a version of the
feature, either closed off or an open wave making its way into
western CO by Sunday possibly bringing increased winds on the plains
and storms for the northern mountains and foothills. This system
will also help to usher in a cool down from the warm temps with
highs dropping into the 70s by Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1023 AM MDT Tue May 22 2018

Denver area airports may see one or two thunderstorms this
afternoon if they drift off the foothills. Storm motions will be
from south to north. Small hail and gusty winds will be the
primary threats. Most shower activity should occur between 3 PM
and 8 PM. South to southeast winds should prevail except for when
showers are present, with erratic and variable winds. Ceilings
should remain above 5000 feet, even as showers move over.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Dankers
SHORT TERM...Entrekin
LONG TERM...Bowen
AVIATION...Dankers


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