IWX issues Area Forecast Discussion (AFD) at Dec 29, 6:21 AM EST297
FXUS63 KIWX 291121
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
621 AM EST Sun Dec 29 2024
.KEY MESSAGES...
- A strong low pressure system will bring widespread rain today
with wind gusts up to 45 mph during the afternoon and early
evening.
- There is a low risk for severe weather in NW OH late this
afternoon.
- Snow may mix in at times this evening before rain ends but no
accumulation is expected.
- More rain on Tuesday before a change to much colder conditions
with possible lake effect snow for the second half of the
week.
&&
.DISCUSSION...
Issued at 242 AM EST Sun Dec 29 2024
Morning water vapor shows very strong circulation currently lifting
out of Arkansas. Given a strong negative tilt and favorable upper
jet dynamics, further deepening of the PV anomaly is expected as it
pivots across our CWA late this afternoon. Leading edge of
isentropic ascent/moisture advection is already pushing into our
area. A very impressive fgen signal is noted moving over our CWA
around 12Z with very steep and strong fgen extending from the
surface through 400mb. Pockets of negative EPV/instability are also
noted above this fgen layer with specific humidities of 6 g/kg
extending to 700mb and 3 g/kg all the way to 500mb. Expect
widespread moderate rain over our area through the morning with
pockets of enhanced mesobanding producing locally heavy rain at
times. This activity will initially be heaviest in the SE but
transition to elevated fgen in our NW by late morning as the
midlevel dry slow moves into our SE around 18Z. QPF totals could
exceed 1 inch in spots just with this morning activity. Ponding in
typical low spots is expected and could lead to some minor impacts
if heavier totals end up over any urban areas. Current RFC river
forecasts keep all river points below action stage at this point.
Forecast becomes even more interesting for the afternoon and evening.
Aforementioned dry slot moves into our SE during the afternoon and
some models suggest a few hundred J/kg of low-topped SBCAPE
developing roughly south of US-24 and east of I-69. IF this does
develop then there will be a risk for damaging wind gusts/possible
tornadoes given very strong 0-1km shear and helicity as well as low
LCL's. The instability signal is very meager though and only shows
up briefly on a few forecast soundings given some lingering capping
concerns and overall poor lapse rates. Confidence in severe weather
is very low but certainly something to watch closely this afternoon.
Of higher confidence is the potential for some brief 45-50 mph winds
in the CAA wing behind passing surface low. Forecast soundings
indicate 45-50kt winds just barely off the surface (as low as
950mb). Mixing will be limited given saturated/stable profiles and
better cross-isobar flow/direct isentropic descent signal is to our
south and southeast, but it won't take much to mix down those gusts.
Expect a swath of brief 45 mph gusts to swing west-east through our
CWA roughly 21-03Z immediately behind the surface low where best CAA
and isallobaric components line up. Best chances for strongest gusts
will be in our SE and after collaboration with neighboring offices
decided to issue a wind advisory for all but our far N/NW where
confidence in 45 mph gusts is lower.
And finally, this push of CAA behind the low could lead to a few wet
snowflakes mixing in. Best chances will be in our north central and
northeast zones where the heaviest precip rates coexist with
slightly cooler profiles/later timing. Any accumulation would likely
be very isolated and melt quickly. Not expected any impacts from
this aspect of the event but don't want anyone to be surprised if
they see some snow mixing in before precip ends late this evening.
After tranquil weather on Mon, yet another robust Pacific wave will
move through the region early Tue. Slightly better agreement on
track and strength but there are still some inconsistencies. Given
plethora of near-term hazards did not deviate far from NBM
initialization. Primarily rain is expected with this event though
surface low track well to our south does raise some questions for
our far northern counties and if precip does linger into Tue night
could see some snow mix in. Overall not a great chance for
accumulating snow but something to watch. Not much change to the
rest of the long term with temps flipping back to below normal. LES
remains possible but still a lot of details regarding fetch and
instability to work out.
&&
.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 618 AM EST Sun Dec 29 2024
Widespread heavy rainfall and gusty winds are on tap for most
of the day today. On radar, widespread rain is lifting through
the area. Ceilings are current on the low end of VFR at KSBN
(but are expected to drop into MVFR in the next few hours) and
IFR ceilings are currently being observed at KFWA. By the
afternoon, I'd expect KSBN and KFWA to have IFR ceilings as
considerable amounts of low clouds will persist across the area
today. Rain will cause reduced visibilities today, down to as
low as 2 to 3 miles at times. Winds will be quite gusty as well,
especially on the backside of the system this afternoon and
evening, with gusts as high as 35 to 40 kts possible (especially
at KFWA). Rain tapers off this evening and dry day is ahead for
Monday.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Wind Advisory from 1 PM this afternoon to 11 PM EST this
evening for INZ008-009-013-015-017-018-020-022>027-
032>034-116-216.
OH...Wind Advisory from 1 PM this afternoon to 11 PM EST this
evening for OHZ001-002-004-005-015-016-024-025.
MI...None.
MARINE...Gale Warning from 10 AM this morning to 9 PM EST this evening
for LMZ043-046.
Small Craft Advisory from 9 PM this evening to 10 AM EST
Monday for LMZ043-046.
&&
$$
DISCUSSION...AGD
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 29, 6:21 AM EST---------------
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!
