Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/27/23

Area Forecast Discussion

National Weather Service Des Moines IA

 525 PM CST Thu Jan 26 2023

...Updated for the 00z Aviation Discussion...

.DISCUSSION.../Tonight through Thursday/
Issued at 301 PM CST Thu Jan 26 2023

Key Messages:

Forecast Highlights:

-Quiet tonight with warming through the overnight
-Light snow moving across the state late tonight through Friday
afternoon
-Accumulating snow expected late Friday through Saturday with better
forcing though location remains a big question
-Cold air returning late Saturday through next week, with wind
chills lowest north

Quiet but chilly weather continued through the morning and into this
afternoon, with plenty of sunshine across much of Iowa with high
pressure currently centered over southeastern Nebraska sliding
east/southeast. Clouds continue to slowly push out of eastern Iowa,
which have allowed for temperatures to be a bit warmer than the rest
of the state in the teens to low 20s. Temperatures otherwise have
slowly risen through the teens for the remainder of the state, with
winds out of the west. The remainder of the afternoon to evening
should remain largely on the quiet side, though cloud cover will
start to expand from west to east ahead of a shortwave and surface
clipper system moving down from southern Canada into the Upper
Midwest. Shifting winds turning southwesterly are also expected
ahead of this system, which is expected to increase temperatures
through the night into Friday morning allowing for a non-diurnal
trend into the 20s and 30s, warmest south.

As moisture advection increases with WAA allowing for good
saturation in the low to mid levels, favorable conditions for lift
and snow production are expected. Guidance generally depicts snow
arriving into western Iowa late tonight, pushing east in a north to
south oriented band through Friday. Guidance overall paints lower
end snow totals across the state, with highest accumulations
generally over northern Iowa before exiting the region Friday
afternoon. There are some differences however between models on
exact snow accumulations, where the NAM and RAP suggest higher
totals nearing 1-2 inches roughly north of Highway 20, with less
than an inch further south. The HRRR, as well as GFS deterministic
and its ensembles however are on a slightly lower trend with the
newest guidance, favoring accumulations largely below an inch across
all of Iowa but with highest amounts to the north. Therefore have
decided not to make any major changes to the forecast as this should
be relatively quick hitting with most areas seeing minor impacts.
Lingering light snow to flurries may continue into early afternoon
before drying out for the remainder of the day. Hazardous driving
conditions are possible for the Friday morning commute, especially
north with slick roads. Periods of blowing snow are also possible as
winds shift northwesterly with gusts generally in the 20 to 25 mph
range, which may allow for reduced visibilities at times.

After a short lived dry period, another surface low sliding east
into the central plains is expected to bring in a better chance for
accumulating snowfall late Friday night through Saturday. Looking at
the features of this system, WAA with increasing saturation in the
column and steepening lapse rates is expected, with mid level
frontogenesis increasing especially through Saturday morning along a
west to east oriented band. Model guidance continues to differ on
the location where the strongest forcing will setup. The RAP and GFS
guidance favors more of a central to southern Iowa setup with
widespread 2-6 inch accumulations across the area, and slightly
lower values further north. On the other side of the coin, the NAM
and HRRR guidance has a strong signal of the fgen zone setting up
over northern into central Iowa, along and north of I-80 with higher
accumulations generally in the 2-6 inch range. Further analysis into
the Euro ensembles places the higher totals also mainly along and
north of I-80, which after considering all these differing solutions
have decided to continue to reflect this trend in the forecast.
Given the overall differences however, cannot rule out further
wiggles in the location of the strongest forcing and therefore
higher snow totals, so it is possible that slight adjustments will
need to be made. Headlines therefore have been held off for now and
will continue to assess these details over the next few forecast
packages. No major concerns are in place for any p-type changes as
temperatures will largely remain below freezing, with the exception
of far southern Iowa where less of the concern for precipitation is
currently in place. Slightly higher SLRs continue to be suggested
among the model members, generally slightly higher than climo in the
15:1 to 20:1 range Saturday. This lighter snow paired with breezy
winds generally in the 20 to 30 mph range will allow for blowing
snow to potentially be a concern as well, but regardless snow
accumulations will again lead to hazardous driving conditions so
extra caution is needed if traveling. Lingering snow may continue
into early Sunday, especially further east as the system slowly
pushes away from the region.

Much colder air moving descending down from the north is expected to
follow as high pressure settles across the region later Saturday
into rest of weekend and through early next week. Temperatures
falling below zero across the northwestern half of the state, and
in the single digits further southeast. This colder air will be
the main story into next week, as lows generally trend in the
single digits to teens below zero and highs in the single digits,
especially Tuesday. Conditions look to be mainly on the quieter
side otherwise, though guidance does indicate low chances for
another round of precipitation Tuesday afternoon and evening with
a system clipping mainly the southeastern half of the state.
Specific details on this are not well known given timing out from
this system but will be more refined over the next several days.

&&

.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 525 PM CST Thu Jan 26 2023

Warm frontal MVFR stratus moving into central Iowa now with patch
to last 2 to 3 hours; briefly breaking to VFR then back down to
MVFR/IFR as main forcing, snow and wind arrive northwest aft 05z.
Hint that stronger forcing visby/cigs may drop significantly for 1
to 2 hours. Have tempos covering lower conditions. Winds to increase
dramatically aft 15-16z north; likely causing more BLSN with newly
fallen and existing snowpack. /rev

&&

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

$$

DISCUSSION...Bury/Cogil
AVIATION...REV



Area Forecast Discussion

National Weather Service Green Bay WI

 553 PM CST Thu Jan 26 2023

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 227 PM CST Thu Jan 26 2023

The latest RAP analysis and satellite/radar imagery show cyclonic
flow continuing over the western Great Lakes early this afternoon.
North flow off Lake Superior helped reinforce the cloud cover
across the region through midday, but clearing has developed
across the Upper Peninsula and north-central Wisconsin early this
afternoon. The back edge of the lingering light snowfall is
moving across central to far northeast WI and is on track to exit
over the next 1-2 hours. Looking farther west, a surface ridge
axis is moving across Minnesota while the next clipper is tracking
from south-central Canada and into North Dakota. As this clipper
moves into the region late tonight into Friday, snowfall timing
and potential accumulations are the main forecast concerns.

Tonight...As deep saturation exits to the east, a surface ridge
axis will slide across northeast Wisconsin during the late evening
into the early overnight. With backing low level winds, the
clearing trends should continue through the evening. Not sure if
winds will decouple for a long enough time for temps to tumble
before clouds quickly return ahead of the clipper system overnight.
As a result, remained conservative with low temps, but did lower
a few degrees in the cold spots. A swath of light snow will then
approach the region in the warm advection zone during the pre-
dawn hours. Timing has slowed down slightly with snow likely
moving into the I-39/Hwy 51 corridor in the 10-12z time frame.

Friday...Low pressure will be moving east across northern Lake
Superior. A swath of QG forcing in a warm advection zone will
push an area of snow across the region from west to east through
the morning before exiting during the afternoon. Forecast amounts
haven`t changed much and most areas will see an inch of snow, with
local amounts upwards of an inch and half. In addition to the
snow, steeping low level lapse rates will support gusty south to
southwest winds from late morning through the afternoon. Northeast
Wisconsin could see gusts as high as 30 to 35 mph. Temps remain
tricky and will remain on the warm side of guidance due to good
mixing. Highs ranging from the mid 20s to low 30s.

.LONG TERM...Friday Night Through Thursday
Issued at 227 PM CST Thu Jan 26 2023

The main concerns in the extended forecast will be the potential
for some light snow Saturday followed by a push of much colder air
that will linger in the area most of next week.

The extended period upper pattern will be relatively static over
CONUS, with a broad upper low over Hudson Bay and a fairly strong
ridge off the Pacific Coast. This will keep mostly northwesterly
flow over our area and allow for a much colder airmass to push in
over the weekend into early next week. This will also be a fairly
dry airmass, so aside from a slight snow chance Saturday, no
major systems are expected to cross the region next week.

As for Saturday, a few light snow showers may still be present
near Lake Superior from overnight Friday, but most of the region
will see a dry start to the day. Then, a passing southern system
will bring just enough overrunning warm air to Wisconsin to see
some increased cloud cover and light snow from southern to central
WI. Overall dynamics seem meager in our area and the general
consensus will still bring a quick inch or so of snow to the area.
Light snow showers will then exit overnight Saturday as the system
moves off to our east.

As mentioned above, following this active weather comes a much
colder and drier period. The coldest day in the forecast will be
on Monday, with highs in the single digits for most of the area
except the lakeshore which will be in the low teens. Highs then
only rise a couple degrees through the upcoming work week, with
highs generally in the teens Tuesday through Thursday. The cold
won`t be around forever though, as long range guidance has begun
suggesting that highs may head back to the 20s and low 30s by next
weekend however. With the fairly cold high temperatures, overnight
lows during this period may see wind chill headlines, especially
for Monday night.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 544 PM CST Thu Jan 26 2023

MVFR ceilings over central and east central WI will gradually
clear from west to east this evening, while VFR conditions prevail
across the north.

A clipper low pressure system will bring snow to the western TAF
sites between 11z-12z/Fri and to the eastern TAF sites between
13z-15z/Fri. The snow will only last about 6 hours at any given
location, and should exit eastern WI mid-afternoon. Widespread IFR
and local LIFR conditions should accompany the snow, with rapidly
improving conditions after the snow ends. Most airports should see
1-2 inches of accumulation, so plowing operations will likely be
needed.

Low level wind shear will overspread the region from west to east
late tonight into early Friday, then diminish in the late morning
to early afternoon. Gusty south to southwest surface winds will
develop ahead of a cold front late tonight into Friday morning,
then become westerly after the front passes in the afternoon. The
gusty winds could cause some minor blowing and drifting of the new
snow on Friday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......Kieckbusch