IWX issues Area Forecast Discussion (AFD) at Dec 2, 4:40 AM EST
934
FXUS63 KIWX 020940
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
440 AM EST Mon Dec 2 2024
.KEY MESSAGES...
- Lake effect snow will become heavy at times later today and
into tonight. 6-9" with locally higher amounts is expected
over Berrien and Cass MI Counties with lesser amounts in
surrounding areas.
- There is still some uncertainty in where exactly the lake
effect snow bands set up and how much snow they will produce.
Stay tuned for updates throughout the day.
- Dry weather returns Tue afternoon-Wed morning but additional
rain and light snow are possible late Wed into Thu.
&&
.DISCUSSION...
Issued at 440 AM EST Mon Dec 2 2024
Overall no major changes to the forecast thinking from yesterday.
Highest confidence in 8+" remains over the eastern half of Berrien
County into NW Cass. Lower confidence in warning-criteria totals for
St. Joseph IN but latest hi-res suggests far northern portions of
the county will get clipped with heavier rates later today. Did
delay the start time for areas outside of Berrien/Cass though. Went
with advisory for northern La Porte, Elkhart, and St. Joseph (MI)
with the lowest confidence on the eastern side of St. Joseph (MI)
and the western side of La Porte. No headlines to the south but may
have to watch northern Marshall and northern Kosciusko. We will
continue to fine-tune the location of the lake effect snow bands
through today and some changes to headlines may still be possible.
Details below...
Morning water vapor shows robust shortwave currently diving into the
Upper Midwest. Low level wind profiles will continue to slowly veer
through tonight as this midlevel trough axis passes and low level
lake aggregate troughing becomes better established. LES which is
currently hampered by WNW fetch, dry air entrainment, low inversion
heights, and overall meager instability will gradually intensify and
organize through tonight. Equilibrium levels still expected to climb
above 10 kft by this afternoon per latest hi-res forecast soundings.
0-2km delta theta-e values also drop below zero by this afternoon
and strong ascent/supersaturation in the DGZ will promote large
flakes and high (potentially over 20:1) SLR's. Of greatest concern
though is the increasing potential for meso-low formation over SE
Lake MI and into Berrien County this afternoon as suggested by
the latest runs of the HRRR and RAP. Already starting to see
some hints of this in latest GRR radar imagery given overall
weak synoptic flow becoming increasingly convergent over the
eastern lake thanks to very warm lake waters/induced troughing.
If this verifies...much higher snowfall totals are likely in the
18-00Z time window. Models have been mixed on whether this
feature drifts far enough south to impact South Bend before
dissipating but latest runs seem to be trending further south
and this was the primary reason for going with a warning in St.
Joseph (IN).
There may be a brief lull in activity during the evening hours
before the low level flow veers further and briefly connects with
Lake Superior during the late overnight hours. Even here some models
are hinting at a "type-VI" (dominant single band with a meso-low on
the southern end) moving down the lake in the 06-12Z period.
Instability parameters remain highly favorable but final lake effect
band intensity and snowfall amounts will be heavily driven by the
degree to which this band can become organized. The biggest negative
factor for this event continues to be the highly variable low level
wind directions. Stronger synoptic flow is anticipated tonight with
only a brief window of favorable down-axis fetch/Superior connection
before flow quickly backs once again Tue AM. Significant questions
remain if this will be enough time to allow a single band to fully
develop, or if (as hi-res models suggest) it is more of a
broken/transient hybrid with pockets of heavier snow and possible
small-scale circulations that never fully organize into a single
continuous band. Either way the chances for heavy snowfall rates to
remain stationary in one particular area for a long time remain low
and warrant a cautious approach to overnight snowfall totals for
now. Additional changes are quite possible as we progress into
tonight though.
Continued to make very few changes to the NBM-initialized long term
grids. LES will end quickly late Tue AM as flow backs SW and dry
conditions will persist trough most of Wed. Highs even climb above
freezing on Wed with some brief but modest WAA. This will be short-
lived though as another deep upper low dives into the Great Lakes
Wed night and sends a strong cold front through the area. Moisture
availability is not ideal but expect some SCT rain showers along the
front followed but blossoming lake effect snow behind the front.
Still plenty of time for adjustments but currently expect strong NW
flow will bring a cold (but dry) airmass with limited fetch for
significant snow accumulations. LES ends by Fri with a longer period
of light WAA expected over the weekend into early next week that
will return temps to seasonal norms.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1155 PM EST Sun Dec 1 2024
StratoCu high MVFR/low VFR layer has been like a permacloud
with undulations over the SBN terminal the past 48 hours. SBN
has just dipped back under 030 and should stay below 030 as the
lake effect snow environment gradually becomes more favorable
for activity. Tried to put some detail with most favorable
activity in the 23Z to 03Z window given the very latest model
guidance. FWA should remain VFR as the snow showers remain west
of the terminal.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 3 PM EST /2 PM CST/ this
afternoon to 10 AM EST /9 AM CST/ Tuesday for INZ005-103.
Winter Storm Warning from 3 PM this afternoon to 10 AM EST
Tuesday for INZ104-204.
OH...None.
MI...Winter Weather Advisory from 3 PM this afternoon to 10 AM EST
Tuesday for MIZ079.
Winter Storm Warning from 10 AM this morning to 10 AM EST
Tuesday for MIZ078-177-277.
MARINE...Small Craft Advisory from 3 PM this afternoon to 3 PM EST
Tuesday for LMZ043-046.
&&
$$
DISCUSSION...AGD
AVIATION...Skipper
Source: IWX issues Area Forecast Discussion (AFD) at Dec 2, 4:40 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412020940-KIWX-FXUS63-AFDIWX)
---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!