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Area forecast discussion
National Weather Service La Crosse WI
639 PM CST Tue Nov 19 2019

Update...
issued at 638 PM CST Tue Nov 19 2019

Areas of fog continue along and east of the Mississippi
River this evening, with a couple of sites already dropping to 1/2
mile or less. Given current trends and with light flow overnight
likely to continue to support fog development, have issued a dense
fog advisory for areas along and east of the Mississippi River in
Wisconsin where short term guidance is most consistent in indicating
fog potential. Will have to monitor trends/guidance tonight for
possible westward expansion of the advisory, but at present
confidence is lower in seeing dense fog west of the river, though
areas of fog will still be possible in these areas overnight.

&&

Short term...(this evening through wednesday)
issued at 216 PM CST Tue Nov 19 2019

Latest 19z surface analysis indicates warm front extending from
northern Minnesota to eastern Iowa. Low level stratus is along and
northeast of the surface warm per latest visible satellite imagery.
Latest metars show temperatures in the middle 40s across northeast
Iowa to the lower 30s across north central Wisconsin.

Tonight...the combination of low level moisture...light winds and
inversion over the forecast area will allow for fog...possibly
dense..to redevelop late this evening into tonight. Latest hi-
resolution models suggest visibility to be reduced to a half of a
mile or less at times. Introduced widespread fog across the area.
Fog may freeze on untreated Road surfaces and create slippery
travel...especially over central Wisconsin.

The 19.12z GFS/NAM are in good agreement lifting warm front north
into northern Wisconsin Wednesday and advect warmer air aloft over
the region. Models suggest 925mb temperatures warm to plus 1 to plus
7 degree celsius. However...the forecast area will remain mostly
cloudy and high temperatures are expected to climb into the upper
30s to upper 40s. Pressure gradient tightens across the forecast
area late Wednesday morning/afternoon and produces breezy
conditions. With the increasing southerly winds...moisture advects
northward after 21z Wednesday. The 19.12z GFS/NAM indicate lift
increases 21z Wednesday to 00z Thursday over the western forecast
area and provide the possibility of light rain into the far western
parts of the forecast area.

Long term...(wednesday night through tuesday)
issued at 216 PM CST Tue Nov 19 2019

A surface low pressure system from the Rocky Mountains of the
southwest will progress northeast though the region overnight
Wednesday into Thursday. Strong southerly winds will pump in warm
moist air into the region making this system anomalously wet. The
GFS, ECMWF, and NAM have precipitable water values slightly
exceeding 1 inch across the region. Typical precipitable water
values for this time of year are around one third of an inch. Rain
will be the main type of precipitation as surface temperatures
overnight remain relatively warm in the mid 30s to upper 40s. A bulk
of that will fall overnight Wednesday, and widespread totals from
0.75 to 1.00 inch are expected. Although unlikely, there is a small
chance that some type of frozen precipitation could mix in over
north central Wisconsin as the tail end of the system moves out.
Before the cooler mid level air moves in, NAM soundings show the
atmosphere drying out pretty quickly after the system passes, so
currently no frozen precipitation is expected.

After the system moves out Thursday afternoon, dry conditions are
expected through Monday, with seasonable temperatures. Precipitation
chances return on Tuesday next week, but timing, precipitation type,

&&

Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 607 PM CST Tue Nov 19 2019

LIFR ceilings and visibilities are expected at klse tonight, with
IFR conditions expected at krst.

Drizzle/fog has been producing visibilities under 1 mile and LIFR
ceilings at klse this evening. Under light surface winds overnight,
not expecting much, if any, improvement in this. Expect IFR ceilings
to continue at krst as well, but potential for fog is less certain
in this area due to slightly more surface flow this
evening/overnight. That said, it's possible areas of fog to the east
of krst may eventually work west toward early morning and have
trended the taf that way. This will have to be watched overnight.
Southeast winds increase Wednesday morning ahead of low pressure
approaching from the southwest. This should help to lift our
morning fog/low clouds, with a transition to mainly VFR clouds by
afternoon. Winds could be gusty at times Wednesday afternoon,
with gusts of 20 to 25 knots possible. Rain chances look to hold
off until Wednesday evening.

&&

Hydrology...
issued at 216 PM CST Tue Nov 19 2019

Widespread rainfall expected Wednesday night into Thursday morning.
An unseasonably moist airmass moves into the region Wednesday night
with precipitable water values climbing into the 1 to 1.25 inch
range. Naefs standardized anomalies climb over 4 during this
timeframe too. The shallow frost in the ground has started to thaw
but the top layers of soil remain wet and won't absorb much if any
rainfall. Any rain that falls will likely runoff creating rises on
area rivers and streams. With widespread 1 inch rainfall amounts,
most areas will see within bank rises, but cannot rule out minor
flooding in some areas. If rainfall amounts increase, minor flooding
will become more likely. Monitor later forecasts and river levels
closely this week.

&&

Arx watches/warnings/advisories...
WI...dense fog advisory until 9 am CST Wednesday for wiz017-029-
032>034-041>044-053>055-061.

Minnesota...none.
Iowa...none.
&&

$$

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