Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/03/19

Area Forecast Discussion

National Weather Service Des Moines IA

 633 PM CDT Sat Nov 2 2019

.DISCUSSION.../Tonight through Saturday/
Issued at 225 PM CDT Sat Nov 2 2019

.Overview...Temperatures through the period will remain at least
5 or more degrees below normal as cyclonic flow persists around an
upper level low pressure over Hudson Bay. Overall, it will be
dry, but there will be passing opportunities for precipitation
including on Sunday/Sunday night, later Tuesday, and later
Wednesday. Toward the end of the period, a quick shot of colder
air will dive into the area followed by a temperature rebound by
next weekend.

.Details...GOES East imagery early this afternoon shows a split
jet stream over the western CONUS with the streams merging to some
degree over the eastern CONUS. Over the upper Midwest, northwest
flow continues with the shortwave that brought the dreariness and
drizzle/light rain on Friday exiting to the east. Heights will be
rising slowly over the next 24 hours or so ahead of the next
shortwave trough that will arrive later Sunday. This will likely
lead to, on average, the warmest conditions over central Iowa for
the next 7 days as temperatures peak in the middle 40s over
northern Iowa to around 50 degrees over southern Iowa. Sunday will
be overall cloudy with cross sections showing a layer of
saturation that develops and deepens in the morning over southern
Iowa and spreads northward through the day. With weak to moderate
omega, expect there will be drizzle or light rain over southern
Iowa later Sunday morning perhaps lingering into early afternoon.
The 12z NAM Nest, WRF ARW and NMM cores, and recent runs of the
RAP all show low chance PoPs so will continue to advertise this
possibility. A better chance of precipitation will arrive later in
the day into the night and be focused over the northern part of
the state as the shortwave arrives with an area of weak low
pressure passing well northeast of Iowa. Forecast soundings show
that there is saturation within the ice introduction layer, but
low levels are expected to be initially too warm for any snow. As
temperatures lower in the evening, a transition to a rain snow mix
and eventually all snow over northern Iowa is expected. Any
accumulations will be confined to elevated and grassy surfaces and
just a few tenths of an inch. With temperatures dipping to near
freezing, elevated wet surfaces may become slick as they refreeze.
Any lingering precipitation will end early Monday morning as high
pressure slides into and through Iowa by early Tuesday.

The remainder of the forecast is currently favoring dry conditions,
though there are a few opportunities for precipitation to brush the
state.  As the high moves to the east Tuesday, return flow and weak
warm air advection may foster a light rain snow mix to all snow late
Tuesday afternoon into Tuesday night over northern Iowa. Another
chance will come later Wednesday as an upper level low pressure
currently off the California coast moves onto the southern Plains.
The highest chance for precipitation will be south of Iowa, but it
could brush southern Iowa with some light precipitation.

As for temperatures, they will certainly be on the cool side for the
first half of the week, but models show potential for a quick shot
of colder air to end the week as a 1040mb-ish high drops down from
the Canadian Rockies and over us Thursday. Looking at a randomly
selected location in southern Iowa for temperatures on Wednesday,
the distribution of guidance is relatively clustered tightly around
a warmer solution compared to the previous forecast and recent run
of the NBM, which fall outside of the IQR. The same is not true at a
randomly selected location in northern Iowa. The distribution is
relatively tightly clustered again, but the previous forecast and
recent NBM are within the IQR and at or near the mean for the
distribution. For Thursday and Friday, the distribution is more
spread with the NBM near the mean over southern Iowa and near the
lower end of the IQR over northern Iowa. Therefore, bumped
temperatures a few degrees over the southern portion of the area
tapering to initial guidance over the north on Wednesday and
remained with initial guidance for Thursday and Friday. While the
week may end with highs in the 30s, heights are expected to rise
over the weekend with temperatures not as cold back into the 40s.

&&

.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 633 PM CDT Sat Nov 2 2019

Winds to become light and variable overnight and shift around to
the south, before then shifting back to the southwest for much of
Sunday. Sct-Bkn mid clouds overnight, then CIGS lowering to low
VFR Sunday afternoon. Could see some gustiness at KOTM with the
winds by Sunday afternoon.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

DISCUSSION...Ansorge
AVIATION...Beerends



Area Forecast Discussion

National Weather Service Riverton WY

 430 PM MDT Sat Nov 2 2019

.SHORT TERM...(Tonight through Monday)
Issued at 353 PM MDT Sat Nov 2 2019

A shortwave in the northwest flow will quickly dive across
northern/eastern Wyoming tonight, with some support from an upper
level jet streak. Snow is expected to develop this evening, and
expand in coverage through midnight over the northern mountains,
along and east of the Divide. There will be a 3 to 6 hour period
where the snow will be the heaviest (still light), as the main
shortwave energy pulls across the area. As this occurs some snow
could impact the adjacent foothills, but current thinking it would
be mainly flurries if it did. In the wake of this shortwave, very
light snow or flurries are expected to continue over the northern
mountains, mainly over N. Bighorn Mountains Sunday in a moist
northwest flow. Elsewhere through Sunday morning, dry conditions
with variable mid-high level cloudiness.

Another shortwave trough in the northwest flow will dive southeast
into the N. Plains/Upper Midwest, sending a weak cold front
south into the the area Sunday afternoon into Sunday night. At
the same time, models in good agreement with a tightening
baroclinic zone in the mid-levels across northern/northeastern
parts of the forecast area. Snow is expected to gradually break
out across N. Wyoming Sunday afternoon and expand in coverage
Sunday evening with the best coverage over the Bighorn Mountains,
Northern Bighorn Basin and N. Johnson County. Snow is expected to
continue through Sunday night, but gradually decrease in coverage
Monday morning as the main forcing shifts away and the area trends
to the anti-cyclonic side of the upper jet. For now keeping the
Bighorn Mts mainly at or below advisory amounts, with lower
elevations an inch or less. One concern in the northwest flow is
for the potential of banding of snowfall in the northern or
eastern areas of the Bighorn Basin where snow totals are isolated
higher by an inch or two. The HRRR and the 18Z NAM12 are hinting
at this possibility.

.LONG TERM...(Monday night through Saturday)
Issued at 353 PM MDT Sat Nov 2 2019

The dominant northwest upper flow over the area will continue
through the extended period. Warmer and dry Tuesday for most of
the area. By late Tuesday night into Wednesday a cold front will
begin pushing down from the north with increased chances of precip
into northeastern Wyoming. While most of the precip should stay
to the north, the Bighorns could see light snow with minor
accumulations through Wednesday. As for temperatures: models
disagree on how far the front will make it on Wednesday but highs
east of the Divide will likely be 10 to 20 degrees cooler than on
Tuesday. Cooler highs continue Thursday before a slight warm up on
Friday. Models hint at a break down of the northwest flow by
Friday which could usher in more active weather for the weekend.
Low confidence for now but have kept higher precip chances across
northwestern Wyoming Saturday into Sunday.

&&

.AVIATION...For the 00Z TAFS through 00Z Monday

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

VFR conditions are expected at terminals through the period. A
period of snow showers are expected in the northern mountains,
especially the Bighorn Mts, between 03Z and 09Z Sunday. Showers
will be hard pressed to push into the foothills. If they do, only
flurries are expected with ceilings and visibility remaining VFR.
Breezy to windy westerly flow will continue on lee side of
mountain ranges into some foothills, as well as from Rock Springs
to Casper. Will have low-level westerly wind shear for the KCOD
terminal, as conditions look similar to what occurred Friday
night.

A weak cold front will push into northern Wyoming Sunday
afternoon, with chances of snow increasing across the far north
especially after 21Z Sunday. Ceilings will be lowering Sunday
afternoon, but are expected to stay VFR in the lower elevations
through 00Z Monday.

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions with variable high-level cloudiness. Wind will be
light except breezy between Rock Springs and Casper, as well as
over ridge tops.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.


&&

.FIRE WEATHER...
Issued AT 353 PM MDT Sat Nov 2 2019

Periods of light snow over the north, mainly over the northern
mountains tonight, and again Sunday night and Monday with the
second system producing several inches of snow in the northern
mountains, but little accumulation over the northern lower
elevations.

Smoke dispersal on Sunday will be generally poor in most areas,
with the exception of areas of fair to good over the western
mountains.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Murrell
LONG TERM...Myers
AVIATION...LaVoie
FIRE WEATHER...Murrell