335
FXUS63 KAPX 041505
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1105 AM EDT Thu Jul 4 2024

.KEY MESSAGES...

- Shower/t-storm chances increase late tonight into Friday.
  Locally heavy rainfall Friday.

- Active weather at times next week.

&&

.UPDATE...
Issued at 1105 AM EDT Thu Jul 4 2024

Synopsis: Large scale pattern features broad ridging from the
southeastern U.S./southern Plains westward into California...west-
southwest mid level flow across the Great Lakes north of this ridge
and ahead of a short wave trough moving through the Dakotas/
Nebraska.  Water vapor imagery also shows a lead short wave trough
from southeast Minnesota/eastern Iowa/Missouri.   1011mb surface low
over far western Minnesota with some semblance of a warm front
extending east into Wisconsin.  Another front stretched from the
lower Lakes into northern Ohio/Indiana/southern Illinois...south of
which dew points were in the 70s.  Good bit of sun to start the
holiday across northern Michigan with temperatures already in the
70s and dew points in the 60s.  More widespread mid/high cloud cover
across Wisconsin was spreading northeast...but closest precipitation
is west of the Mississippi and south of Lake Michigan with a
"bubble" of drier air (in a relative sense) over Michigan/northeast
Wisconsin eastward into the lower Lakes.  12z APX sounding reflects
this with >15C dew point depressions above 800mb.  Boundary layer
mixing ratio also drops quickly off the deck (near 11g/kg at the
surface to around 8g/kg in residual layer evident from 900-800mb).

Forecast Update:  Only concern for the afternoon will be lake breeze
development and whether any convection will pop along these
boundaries over eastern Upper and on the Lake Huron breeze south of
Thunder Bay.  Dew points are expected to mix down into the 50s for
the most part away from the lakes...so only moisture convergence/
onshore flow along these boundaries will keep dew points high enough
to squeeze out a modicum of MLCAPE (100-200J/kg).  Added lift from
short wave trough coming out of the upper/mid Mississippi Valley
won`t hurt the cause either especially across Upper Michigan.
Background northerly flow will push Lake Superior breeze farther
inland so best chance for any development north of the Bridge would
be across Mackinac county. A low (but non-zero) probability event
for sure.  Already setting up to be a warm afternoon with 70s across
eastern Upper and 80s across northern Lower away from the lakes.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 343 AM EDT Thu Jul 4 2024

Happy 4th of July.

Pattern/synopsis: Low pressure over Hudson Bay will move ne-
ward. There are multiple surface trofs moving thru the northern
lakes, but the departing low will leave behind w-e oriented
troffing over the central lakes. Part of this can already be
analyzed as a warm/stationary front from eastern SD to central
WI. Aloft, a digging shortwave is likely to close off as it
transits southern MN tonight.

Forecast: Isolated showers are being maintained along a surface
trof that extends from south of LDM to north of APN. These will
persist for a few more hours, as they move eastward. Otherwise,
there are patchy mid clouds over eastern upper and ne lower MI.
Early on, surface heating will be relatively uninterrupted, and
temps will climb quickly this morning. We remain muggy (surface
dew points 60-65f), and that heating will eventually result in a
cu field. A partly cloudy afternoon is expected. Temps are warm
enough aloft to keep most of northern MI with minimal Cape. But,
where lake breezes move inland, and where moisture pooling
occurs along them, we may realize up to 300j/kg of MlCape. The
areas of interest are the interior of eastern upper MI, and ne
lower MI from Rogers to Standish. Isolated showers here are
maybe possible, late this afternoon into this evening. The grids
will have POPs around 10 percent, but this is not enough to
include a mention of a shower.

Tonight: as the upper low crosses southern MN, a weak surface
wave should take shape just ahead of it. A warm front sharpens
to the east of this (especially aloft), over southern WI. The
low level jet in the area is weakish, but a very rich airmass is
in the warm sector. Beginning late today, deep convection
should continue to generated in parts of MN/IA, and eventually
WI. Moisture/forcing/instability are all better west of Lake MI
than east, and CAMs are disagreeing considerably as to how far
east precip will get. Have kept the evening dry, before shower/
t-storm chances increase overnight. Highest pops are after
4-5am, west of I-75 in both peninsulas. Respectable precip rates
are possible...but are much more likely to be realized on
Friday and beyond.

Max temps mid/upper 70s north, to upper 80s far se. Lows mid 50s
to mid 60s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 343 AM EDT Thu Jul 4 2024

Primary Forecast Concerns/Key Messages:

Midlevel split flow pattern for the first half of the long term
followed by broader troughing next week will continue chances
of showers and storms at times throughout the entirety of the
forecast period. Embedded shortwaves will produce the best
chance of widespread rainfall across the CWA this weekend and
early next week.

The first trough with relatively weak surface low pressure currently
over the northern planes will progress to the Upper Midwest by late
Thursday night. The second main round of showers will not arrive
until Tuesday as an additional trough moves across the upper Great
Lakes region.

Primary Forecast Concerns:

Showers and storms return this Friday. Locally heavy rainfall
remains possible: Latest ensembles show weaker forcing compared
to past model runs along with lower H8 winds. With more
potential atmospheric stability and less southerly moisture
feeding into the CWA, lower QPF can be expected. The disheveled
core of low pressure is expected to track across central
Michigan, delivering a general half inch or so of QPF, but
locally higher amounts can be expected as PWATs remain quite
juicy (well over an inch).

Longwave troughing will keep chances of active weather at times
next week: Aformentioned split flow followed by longwave
troughing across the northern half of north America will keep
active weather at times for the remainder of the forecast
period. Best chance of widespread rainfall is on Tuesday as
another shortwave drops from northern Hudson Bay to the Upper
Great Lakes. Longwave troughing after Tuesday will keep chances
of diurnal pop-up thunderstorms like a typical northern Michigan
summer.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 656 AM EDT Thu Jul 4 2024

A touch of fog to start the morning at CIU and PLN, but that
will burn off very quickly. Quiet today, though a cumulus field
at 4-6k ft will form by afternoon. Not expecting any precip at
the TAF sites. Tonight, high clouds increase ahead of our next
system. There`s a chance for showers, mainly after 08Z, with
more widespread rain during the day Friday.

Light winds today, with onshore lake breezes this afternoon.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...JPB
SHORT TERM...JZ
LONG TERM...SJC
AVIATION...DJC/JZ