Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 120337
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1037 PM CDT Mon Mar 11 2024

.KEY MESSAGES...

- Record Breaking Warmth Continues Through Tuesday.

- Precipitation Chances Return Wednesday Night Through Thursday.
  Type Remains In Question With Higher Chances For Snow In
  Central Wisconsin.

&&

.DISCUSSION...
Issued at 244 PM CDT Mon Mar 11 2024

Synoptic Setup Today:

Record breaking warmth continues for Tuesday and Wednesday as
heightening isoheights persists return flow. GOES 16 Water
Vapor imagery and derived winds exhibit quite a progressive
pattern with amplifying upper level jet streaks up and
downstream. As a result, the overhead and upstream upper level
anticyclonic flow has been progressing across the Upper
Mississippi River Valley with a quickened step. Open level
waves evident in upstream GOES water vapor imagery loops are
expected to split further, splitting across the Upper
Mississippi River Valley overnight tonight into Tuesday morning.

Temperatures Through Wednesday:

The southern upper level wave digs through the South-Central Plains,
bolstering local low level return flow while the northern upper
level perturbation phases through the northern Great Lakes. As
a result of these locally avoidant and progressive
perturbations, a tightened surface pressure gradient and
intensifying low level jet will persist gusty conditions through
much of Tuesday. The separation between streams drops a low
level frontal boundary zonally bifurcating our southern
counties. A lack of upper level forcing through the end of the
week results in this boundary residing through and along our
southern half from northeast Iowa into southwest Wisconsin
through Thursday. Therefore, as the warm sector contains
anomalous temperatures with an enhanced north to south gradient,
temperatures will be an ongoing forecast challenge. Support
from both the north and south will only reinforce this estranged
boundary whilst diurnal mixing may also volley it north and
south.

Have continued similar to previous forecasts flirting the 70
degree isotherm for much of the area Tuesday and Wednesday. The
60 degree isotherm expected to lie south of the area Thursday.

Synoptic Precipitation Setup Latter Half of the Week:

While passing northern and southern upper level perturbations
overnight tonight into Wednesday morning will remain dry, a leftover
surface boundary will provide precipitation chances Wednesday night
through Thursday. Similar to last week, the stationary low level
boundary will zonally bifurcate the forecast area through
Wednesday as diffluent, anticyclonic upper level flow advects
over the Upper Mississippi River Valley and anticyclonic flow
sags south out of southern Canada. A resurgence in upper level
winds late Wednesday places an area of increased divergence in
the exit and entrance regions of a dual jet streak with upper
level diffluent flow through the Central Plains.

Precipitation Types and Surface Low Progression:

As a result, a surface low traverses northeast form the Central
Plains into the Upper Mississippi River Valley. Again, similar to
last week, the low level isoheight straddle and accompanying
stretching zone supports low level deformation from central
Minnesota through central Wisconsin. The overnight passage of the
extratropical cyclone from southwest to northeast advects the
freezing isotherm from southeast Minnesota through central
Wisconsin early Thursday morning. Cannot rule out thunder as
well closer to the low as the main energy reaches northeast Iowa
within the nose of the increased low level theta e lobe and
occlusion zone.

Consistent with previous forecasts and long term global ensemble
model confidence (EPS/GEFS 11.12Z), have increased and added snow to
the weather grids Thursday night into Friday morning as the low
departs east and cold air advection further supports frozen
precipitation. Overnight timing and location of the surface low
responsible for the increased moisture advection will be the
utmost important forecast details for precipitation type and
thunder chicanes.

Into The Weekend Temperatures & Precipitation:

Into the weekend, a subsequent longwave positively tilted trough
sags southeast from southern Canada through the Upper
Mississippi River Valley, removing any lingering boundaries and
more anomalous temperatures from the area. Slight precipitation
chances dot through the weekend as the longwave trough
progresses southeast.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1037 PM CDT Mon Mar 11 2024

A period of low-level wind shear will occur overnight tonight as
winds off the surface increase. Otherwise, VFR conditions will
persist with some periodic high clouds. A front will swing
through Tuesday morning with winds becoming NW.

&&

.FIRE WEATHER...
Issued at 322 PM CDT Mon Mar 11 2024

Relative humidities have relatively behaved compared to the
overnight forecast with minima of the teens along western
peripheral counties in southeast Minnesota and northeast Iowa.
Increased surface winds sustained through the late morning,
eventually dropping off and reducing any elevated fire weather
concerns in our far western counties.

Similar concerns expected for Tuesday primarily in central
Wisconsin with the sandier soils and a southerly sagging dry
airmass. A tightened surface pressure gradient and nocturnal low
level jet will sustain southwest surface winds above 15 mph
early Tuesday morning before a dry frontal boundary rotates
these winds to northwest. Again, higher confidence for elevated
fire weather concerns remain in central Wisconsin where a
similar situation as today with increased mixing may bring RHs
into the teens as low 20s are currently forecasted. The more
moist air mass from northern Iowa into far southern Wisconsin
will be a finer forecast detail that will also impact mixing and
any resultant parameters (smoke dispersal, winds, dewpoints).

&&

.CLIMATE...
Issued at 244 PM CDT Mon Mar 11 2024

The following are record high temperatures at La Crosse and
Rochester for today and Tuesday along with the current
forecast. As of 230 pm CDT, Rochester has reached 70 degrees
and La Crosse has reached 64 degrees. This is a record for
Rochester by 1 degree, and 6 degrees short of the record at La
Crosse. Temperatures are expected to continue warming with low
level warm air advection ramping up this evening and will be
something to continue to monitor. Exceedance probability at La
Crosse remains 70-80% for today. Exceedance probability
tomorrow is 50% at Rochester and 30% at La Crosse.

                    Today                Tuesday
Location       Forecast / Record      Forecast / Record
-----------------------------------------------------------


La Crosse           70 / 67 (2012)         72 / 74 (1990)
Rochester           70 / 63 (2012)         67 / 67 (1990)

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...JM
FIRE WEATHER...JAR
CLIMATE...JAR


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