Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 282214
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
514 PM CDT Thu Mar 28 2024

.KEY MESSAGES...

- Several Degrees Warmer Through Friday With Precipitation
  Chances Returning Friday Evening Into Saturday Morning

- Wintry Mix Likely In Central Wisconsin Through The Overnight
  Hours, Freezing Rain and Sleet Potential Remains Possible In
  Smaller Area of Northeast Taylor County

- Low, Minimal Precipitation Chances This Weekend, Increasing
  Early Next Week

&&

.DISCUSSION...
Issued at 256 PM CDT Thu Mar 28 2024

Synoptic Setup & Temperatures Through Friday Afternoon:

An upper level trough, associated and downstream of the closed low
off the Pacific Northwest Coast on GOES Water Vapor imagery this
afternoon, is expected to further separate and lift through the
Northern Plains through Friday, providing local precipitation
chances Friday night. The closed low is completely wrapped, as
GOES derived upper level winds are acting to separate the
northern stream. This (northern) perturbation will combat broad
upper level anticyclonic flow. As seems to be the theme, or
simply a Baader-Meinhof effect, primary impacts expected to
skirt north & south of the forecast area: balderdash.

The strong anticyclonic flow and impending precipitation will
advect a warmer airmass through Friday afternoon. While tapping
into the highest temperature airmass will remain to the south,
temperatures will be several degrees above today.

Initial Precipitation Chances Friday Evening:

Northern precipitation bears a northeastern trajectory as the
enhanced subtropical jet, poking into Southern California on
GOES 17 derived winds this afternoon, will shunt this synoptic
forcing northward. Current confidence in long term, global
ensembles (GEFS/EPS 28.12Z) places resultant upper level
convergence initially. The weakening, lifting forcing will
initially provide meager precipitation chances along the
increased isentropic upglide and warm frontal boundary. This
initial wave struggles to initially saturate farther south,
placing Medford, WI with highest confidence locally for any
precipitation chances. With the drier air, have held off
slightly for precipitation onset compared to National Blend,
delaying into the nighttime.

Higher Precipitation Chances Overnight Friday Into Saturday:

Irregardless, the resident more moist, warm airmass resides across
the forecast area into the nighttime, fueling subsequent
precipitation chances. The responsible follow-up forcing in the form
of double barrel surface lows churn across the Upper Mississippi
River Valley through the overnight. The northern low occludes
the warm sector while the southern low forms along the
accompanying triple point, following the low level baroclinic
boundary. As a result, best precipitation chances slide along
our northwestern and far southern peripheries into Saturday
morning. Have slightly accounted for this in afternoon forecast
package, using higher confidence within high resolution, short
term model guidance for highest PoPs northwest, south, and east
of the local forecast area.

Thunder Chances:

The southern stream will contain some MUCAPE and thunder firing off
the nose of the low level jet. The shunting of the low level jet
nose and to the south and overnight timing of best forcing locally
limits confidence and coverage locally. Have continued with National
Blend Probability of Thunder which dabbles Thunder chances along
our southern edge primarily in Grant County, WI.

Potential Wintry Mix Remaining In Taylor County:

Precipitation type remains a challenge locally in northern
counties of central Wisconsin. The closure of the warm sector
drops surface temperatures quickly below freezing whilst
moisture and warm nose lingers off the deck. In other words,
discerning the mesoscale timing and location of the warmer,
above freezing air as well as lowest level, below freezing cold
air remains in question. High resolution soundings differentiate
in timing by a couple of hours as well into early Saturday
morning. Daytime high temperatures through Friday which will
also be of utmost impact to freezing road potential. Have also added
slight mention of Ice Pellets as negative energy of low level
cold air may be enough to refreeze while upper level ice
remains. However, as wee hours of Saturday morning linger on,
upper upper and mid level subsidence increases confidence in
removal of upper level ice and Freezing Rain potential.
Therefore, have continued mention and accumulation in
northeastern Taylor County into Saturday morning.

This Weekend & Early Next Week Precipitation Chances:

The Friday separation of streams provides some disagreement in
forecast details through the weekend into next week. The initially
closed low wobbles through the stages of a well-pronounced
trough into the Southern Plains this weekend before eventually
rejoining parent upper level flow mid next week. Therefore,
increased precipitation chances return early next week as the
trough rejoins the upper level flow. Highest confidence for mid
level heights <540 decameters remains 50-80% along and east of
the Upper Mississippi River Valley. There is also low
confidence for minimal precipitation chances through the weekend
as upper level heights combat troughing and ridging across the
Upper Mississippi River Valley.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 514 PM CDT Thu Mar 28 2024

CIGS: mostly SCT high clouds into Fri afternoon, although could be a
few hours BKN 8-10kft in the morning. Cigs start to settle in moving
into the evening, dropping to lower VFR with an increasing potential
for MVFR overnight. These lower cigs could then hang around for the
better part of Sat.

WX/vsby: upper level shortwave trough set to slip across the region
on Friday will bring areas/scattered showers to the region (rain
south, wintry mix-snow north). However, current track and the outlay
of the various forcing mechanisms and moisture transport suggests
that impacts to the TAF sites could be minimal. Latest meso model
guidance hold most development til around 00z Sat, generally north
of I-94 with another focus over eastern IA/northern IL. In these
scenarios, KLSE might have a few hour shot for -shra while KRST
stays dry. For now will trend the forecast dry and adjust if later
model runs suggest different.

WINDS: northwest winds light easterly overnight. Winds should start
to pick up toward 12z Fri, generally east/southeast through the day
Friday. A few gusts possible, moreso KRST.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...JAR
AVIATION...Rieck


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