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Area forecast discussion 
National Weather Service La Crosse WI
538 PM CST sun Nov 29 2015

Short term...(this evening through monday)
issued at 309 PM CST sun Nov 29 2015

Let the fun begin. Quite the challenging forecast in terms of
precipitation type from late tonight right on through Monday
night...which unfortunately continues to lead to lower than desired
confidence on any snow and/or ice amounts. With that said...there
does seem to be a growing consensus that this storm will be more of
a "slop fest" across the County Warning Area...with pretty much any and all
available wintry precipitation types expected to fall in some part of the
area. One trend that is notable is the earlier arrival timing of
precipitation...with upstream radar trends already quite telling with an
initial band of warm advection-driven precipitation rolling northward
through southern Iowa. Based on that notion and with pretty good
support from short term guidance...getting a little concerned for a
period of sloppy wintry mix rolling through at least a portion of
the County Warning Area toward or just before sunrise Monday. Thermal profiles would
support a mix of sleet or freezing rain at the onset with a notable
warm nose pushing 2-3c...though probably with a fast trend toward a
mix with snow as we wet bulb that layer more isothermal down to
about 0-0.5c. Don't foresee amounts being anything too high during
this initial surge...but with temperatures overnight likely to hang below
freezing...there is a potential impact for the morning commute on
Monday as it only takes light amounts to cause some issues.

Stronger shortwave energy rounding the base of the closed rockies
low will be swinging northward in our direction Monday morning. All
the while...with increasing middle level difluence and left exit region
jet dynamics working in tandem with increased low/middle level warm
advection ascent and decent moisture...we should see a larger precipitation
shield expand northward into the area later Monday afternoon and
evening. By this appears we will draw in abundant warm
air in the developing trowal feature to largely switch the precipitation
type over to rain or a rain/sleet mix. That is especially true over
the majority of Wisconsin counties and even out toward the Highway
63 corridor into southeast Minnesota and northeast Iowa with 800mb
temperatures warming to as high as 4-5c. With that the west we
will have to be concerned about surface temperatures as they will likely
run very close to freezing...thus with a periodic freezing rain
threat. Cips analogs are in pretty good agreement with that
potential for a time. Even farther north/west of a rough line from
Medford to Dodge Center to Austin (and especially along/west of I-
35)...still thinking this will be a mainly snow event...though one
characterized by low ratios with only a narrow dgz and plenty of the
cloud depth only around -10c or warmer...suggestive of lots of
Snowflake riming potential.

Whatever plethora of precipitation types there are out there should
come to an end quickly later Monday night into the first part of
Tuesday morning with the arrival of pronounced dry slotting. With
that said...moisture depth still up to around 750-800mb in that dry
slot with some weak low level lift does at least introduce the
potential for some drizzle and/or freezing drizzle pending surface
temperatures. Deeper moisture wrapping back into the area later Tuesday
into Tuesday night should swing an area of some light snow back
through many areas...but with only minor accumulation expected as
surface temperatures for many areas hold near or just above freezing.

So...what to do with headlines? Based on current
gut feeling is this looks like a longer duration advisory event...
with the heaviest snow accumulation of 3 to maybe 6 inches confined
to far western and northern areas...and falling over a period of 24
hours or so. advisory seems quite warranted. But what to
do with other locations? With low confidence and still lots of
questions about precipitation types...feel compelled to remain headline-
free and allow later shifts to pick up on any near term trends. If
nothing else...we may need to hit the morning commute with an Special Weather Statement or
short-fused advisory if we can realize enough coverage of wintry

Long term...(monday night through sunday)
issued at 309 PM CST sun Nov 29 2015

Thankfully not much to talk about as we get into late week and next
weekend...with the gradual departure of our closed low through the
northern Great Lakes later Wednesday. Starting to look like we may a
low cloud issue into the day on Wednesday with plenty of sub-850mb
moisture trapped beneath a rather sharp inversion as warmer air
starts to flood in aloft. That warming trend aloft will continue
into late week as we see heights really rebound over the plains and
eventually much of the advance of another modest upper
trough working through the western Continental U.S.. despite limited mixing
given the time of year...still really like the notion that many
spots will make a run into the 40s both Friday and Saturday when
925mb temperatures peak out in the 2-6c range. Of course...we will have to
take any snow cover into likely a little cooler for
western/northern areas where the best snow is expected currently.
Otherwise...with limited moisture availability given a largely
closed Gulf of Mexico...just not feeling any decent rain chances
throughout the entire extended forecast...even with the arrival of
that western trough toward Sunday...though there could be a few
bouts of middle/high clouds at times. Overall...just a really nice
period of mild early December weather - we'll take it!


Aviation...(for the 00z tafs through 00z Monday evening)
issued at 538 PM CST sun Nov 29 2015

A complex storm system will impact the upper Mississippi River
valley over the next 24 to 48 hours. Multiple taf updates are
likely through this period. For now...VFR conditions will continue
at klse/krst through at least 30.09z with light easterly winds.
Late tonight into Monday morning...expect the first wave of precipitation
to move northward and across taf airfields. For simplicity...will
keep this precipitation as -rasn at klse and -sn at krst...although an
additional mix of -fzra/pl is possible if warmer air aloft moves
in earlier. Will keep with the idea of lowering ceilings into the
MVFR range through the period with precipitation changing over to all
rain at klse and rain/snow at krst by Monday afternoon. Confidence
in timing of lower ceilings is low...but think IFR conditions will
not develop before 01.00z.


Arx watches/warnings/advisories...
WI...Winter Weather Advisory from 6 am Monday to midnight CST Tuesday
night for wiz017-029-032>034.

Minnesota...Winter Weather Advisory from 6 am Monday to midnight CST Tuesday
night for mnz079-086>088-094-095.

Iowa...Winter Weather Advisory from 6 am Monday to midnight CST Tuesday
night for iaz008-009-018-019.



Short term...Lawrence
long term...Lawrence

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