Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231949

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
249 PM CDT Fri Mar 23 2018


Tonight and Saturday...Forecast Confidence is medium.

A shortwave trough will gain amplitude while progressing from the
Four Corners region into the mid/upper Mississippi valley.
Surface low pressure will accompany the wave, while passing to our
south through the lower Missouri valley. As noted in the previous
discussion, synoptic forcing for ascent is quite strong, yet the
increasing deep layer moisture will be undercut by dry easterly
flow during the event. This will keep snow from this system
mainly confined south and southwest of our forecast area, with
accumulating snow perhaps edging into southwestern portions of
Lafayette county.

The 23.12z model suite appears to have initialized well, with
good agreement on the placement and strength of surface and upper
level features. This agreement generally holds through the
forecast period, although the GFS develops a strong pressure
rise/fall couplet north of the low which appears to result from
convective feedback. The synoptic scale models generally produce
between 0.1 and 0.25 inches of QPF in far southwest Lafayette
County, which, given 10:1 to 11:1 snow ratios would translate to
a 1-3 inch snow accumulation. However, recent RAP and HRRR
solutions suggest the possibility that our area could miss out on
snow entirely as the precipitation remains just to our southwest.
This is unfortunately one of those cases where our southwest is
straddling the snow/no snow cutoff from this system, with similar
probabilities of seeing either a fast accumulating wet snow, or no
snow at all. Regardless, any snow that does fall should be
tapering off by Saturday morning.

Saturday night through Sunday night...forecast confidence is high.

The Hudson Bay High will re-exert it`s dominating influence during
this period. Look for dry conditions, mostly clear skies and temps
close to a bit below normal.

Monday through Tuesday night...Forecast confidence is high.

The scenario for this period remains unchanged. The upper level
ridge slides east while a very large trough digs from central
Canada southwest to the 4-corners region of the U.S. This puts us
in a very active, milder and more moist southwest flow. Model
guidance shows lots of noise in the shortwave energy progressing
northeast into the Great Lakes ahead of the main upper trough
that comes through Tuesday night. Therefore, we should see on and
off rain from later Monday afternoon through Tuesday night.
Precipitable water values increase to around 1 inch with the best
chance for precipitation showing up late Monday night in Tuesday.
The surface front comes through Tuesday afternoon into early
Tuesday evening. There is some CAPE showing up on the soundings,
so will maintain the small chance of thunder on Tuesday.

Wednesday through Friday...Forecast confidence is medium.

The trough will be moving off to the east with high pressure
pushing in. This period should generally be dry, though there is
some small model discrepancy for Thursday that results in a slight
chance of rain. Temperatures will be cooling down as we head
toward the end of next week.


No change to aviation concerns. VFR conditions are expected at
the TAF sites through the TAF period. MVFR CIGS and IFR VSBYS
could move into areas well southwest of Madison between 06-18z
Saturday as low pressure brings a swath of heavy snow to areas
mainly west of Wisconsin. Look for winds to remain steady out of
the east northeast through the TAF period, becoming gusty at 15 to
25 knots later tonight through Saturday.



Look for onshore flow with gusty winds developing tonight. These
gusts will persist over the weekend, resulting in building wave
heights into Sunday. A small craft advisory remains in effect
during this time.


LM...Small Craft Advisory from 10 PM this evening to 1 PM CDT Sunday
     for LMZ643>646.



Tonight/Saturday and Aviation/Marine...SPM
Saturday Night through Friday...Davis is the U.S. government's official web portal to all federal, state and local government web resources and services.