IWX issues Area Forecast Discussion (AFD) at Dec 16, 12:19 PM EST897
FXUS63 KIWX 161719
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1219 PM EST Mon Dec 16 2024
.KEY MESSAGES...
- Rain showers are expected today with areas of fog through at
least the mid afternoon. Patchy dense fog is likely this
morning.
- There are chances for rain and snow Tuesday night into
Wednesday, then chances for lake effect snow Thursday night
into the weekend.
- Highs today will be in the 50s, then drop into the upper 30s
and low 40s for Wednesday. Lows will be in the 30s. Highs this
weekend may only reach into the 20s and low 30s, with lows in
the teens and 20s.
&&
.DISCUSSION...
Issued at 551 AM EST Mon Dec 16 2024
Fog and increasing rain chances are the focus for the short term,
with a warm front just south of our CWA extending from a surface low
over western IL into southeastern IN, in addition to an occlusion
extending northward to a more defined low over MN/Northern Ontario.
The Canadian low will drift eastward into James Bay by 6z Tuesday,
bringing the occluded front across our area today. At the same time,
the low over IL will ride northward along the front, with the triple
point moving along the Michigan/Indiana/Ohio border by this
afternoon/evening. In the west half this morning we're seeing
increased divergence aloft as we're within the right exit region of
a cyclonically curved jet (250-300mb), and a 500mb trough is
approaching from the west. Moisture transport has been slowly
increasing, though it seems that we may be at our maximum through
around 12-15z before the best transport is shunted eastward. I
suspect it's being limited somewhat by the convection south of IND-
which was a concern earlier on this week with regards to this
system. Have likely/cat pops still-especially along and south of US
24 where the better moisture transport exists through the day.
Lowered the QPF from previous forecasts, however. New totals look to
be between 0.09" (far NW near Benton Harbor, MI) to 0.31" (far SE
near Lima, OH).
Fog forecast is tricky. Opted to let the dense fog advisory expire
despite a few locations still suggesting around 1/4 to 3/4 of a mile
visibility at times (mainly in the NE near Hillsdale down southwest
through Warsaw and Rochester). Visibilities have been improving for
many areas in the southeast over the last hour or so-with even
Toledo popping up to 3SM, Coldwater, MI at 1SM, and Fulton, OH at
1/2SM now. Have an SPS out until just after 8 am, when we can re-
evaluate the situation. It's possible we need to re-issue a dense
fog advisory further west sometime late this morning/early
afternoon. Near the occlusion (over western IL) visibilities are
near zero, and this may persist as the boundary moves into our area.
NWS LOT has a dense fog advisory up to our border to cover for this
potential [low/med confidence further east]. Complicating factors
include: increasing pressure gradient as the surface trough impinges
on our stubborn high pressure off the NE CONUS. By the afternoon,
locations further east could be gusting up to around 20 mph at times-
which will make it less favorable we see continued foggy conditions.
Where exactly the gradient sets up between lighter/gustier winds is
in question. Also, how much mixing will we really do today given
extensive cloud cover and "soupy" start to the day. The other
question is how will rain showers impact visibility: sometimes we
see improvement with rain and then conditions drop back down again
after the rain passes. Rain is currently developing over the western
half as of this writing, so we'll see how things trend before we
decide on headlines (if any). Kept areas of fog in the forecast
through 18z, then went patchy afterwards for now. Gusty westerly
winds behind the boundary should keep visibility up through the
night for most areas (and drier air advects in).
As for temperatures, we're already in the mid to upper 40s south of
US 30, the low to mid 40s further north. Have high temps today
reaching into the low to mid 50s, warmest south of US 24. Lows
tonight will be in the 30s.
Zonal flow/slight ridging and a surface high build in behind the
exiting system tonight into Tuesday evening, keeping our area dry
with partly to mostly cloudy skies. Highs will be in the upper 30s
and low to mid 40s. Lows will be around 30 degrees. A deepening
trough in the mid levels will move from the plains states into the
Great Lakes region Tuesday night into Wednesday, then encompass the
entire SE CONUS by 00z Thu. The surface low develops over TN by 12z
Wed, then lifts northeast into WV/KY/SE OH by 18z-then deepens
further as it moves along the eastern seaboard Wed Night. Similarly
to today's system, I suspect the better moisture transport will be
cut off or limited by the convection/precip with the low to our
south. Also like today, we have two phasing features. A decaying
cold front extends from central Ontario across Lower MI and into
Lake MI by 12z Wed...right as the surface low to the south is
reaching into KY. Expect a similar evolution to today's system as
the better moisture is shunted east and the cold front passes
through during the day. With temperatures ranging from the low 30s
to the mid to upper 30s-expect a rain/snow mix. It's possible we see
minor accumulations, though they won't be long lived. Have low to
mid range chances for this period given uncertainties re: moisture
transport and phasing features.
Dry conditions prevail for Wed night into mid-late afternoon Thu
with high pressure building in and relatively zonal/slightly ridged
flow aloft. Lows will be in the 20s and low 30s. Highs will be in
the 30s.
A clipper system enters the Great Lakes sometime around Thu
afternoon/evening, crossing our CWA Thu night into Friday evening,
with high pressure building in behind it. We'll see chances for snow
with this system (30-60 percent in forecast atm). Lake effect may
persist through the weekend in areas favored by N-NW winds as
cyclonic flow lingers aloft until Sun afternoon. High pressure and
dry air build in at the surface gradually through time-and finally a
ridge aloft by Sun afternoon or evening. High temperatures this
weekend will be in the 20s and 30s, with lows in the teens and
20s.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1213 PM EST Mon Dec 16 2024
Rain showers are moving out of the area, just east of KFWA at
the time of this writing. Areas of drizzle and dense fog will
remain through the evening. Visibilities are currently IFR at
KSBN down to 2 miles, which is likely to persist over the next
few hours. The NBM shows about a 60% chance for MVFR
visibilities and a 30% chance for IFR visibilities. KFWA may
also see some fog but visibilities are more likely to be in the
MVFR range. I'd anticipate that as winds increase out of the
west this evening for the fog to dissipate by 00Z tonight.
Wiinds will be quite gusty this evening and overnight, with
gusts 25 to 30 kts possible. Satellite imagery also shows low
and mid level clouds across the area; IFR to MVFR ceilings will
prevail this evening. Clearing is expected to occur overnight,
with VFR ceilings and some sunshine for Tuesday!
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Dense Fog Advisory until 5 PM EST this afternoon for LMZ043-
046.
Small Craft Advisory from 4 PM this afternoon to 4 PM EST
Tuesday for LMZ043-046.
&&
$$
DISCUSSION...MCD
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 16, 12:19 PM EST---------------
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