767
FXUS63 KAPX 182300
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
700 PM EDT Tue Jun 18 2024

.KEY MESSAGES...

- Chances of showers and storms tonight and Wednesday.

- Heat continues...periods of relief at times...

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 359 PM EDT Tue Jun 18 2024

Pattern Synopsis/Forecast: 18z surface analysis shows a pair of
surface lows west/northwest of the Great Lakes...999mb low over
northwest Ontario...trailing cold front to the southwest to a 997mb
low along the South Dakota/Minnesota border.  A more consolidated
warm front extends east of the Ontario low into northern Quebec. The
dreaded apocalyptic "heat dome" is centered over the mid Atlantic
with deep southwest flow around its west side bringing warmth and
moisture into the Great Lakes.  Water vapor imagery shows a compact
vorticity center lifting northeast across western Lower Michigan...
spreading a mostly mid/high cloud deck and some high based radar
returns across northern Lower Michigan.  But it has also helped
sprout a thunderstorm adjacent to Saginaw Bay.  Temperatures have
mostly leveled off across northern Lower with arrival of cloud
cover...areas that have remained in the sun longest from the tip of
the mitt around the northeast Lower shoreline have warmed into the
90-95 degree range...93 at PLN ties the record high for today.

While the upper anticyclone to the east holds firm and pushes the
594DM height contour into southeast Lower Wednesday...upstream cold
front eventually nudges into northern Michigan Wednesday afternoon.

Primary Forecast Concerns:

Rain chances tonight and Wednesday: Initial rain chances this
evening mostly tied to the diurnal heating/instability cycle and
aforementioned passing short wave trough that should be crossing
Lake Huron by early/mid evening.  Once we get this initial activity
out of the way should see a lull in the precipitation chances (and
clouds for that matter) heading into the early morning hours.  But
there also appears to be some gravity waves crossing Wisconsin in
visible imagery...moving into an uncapped 2000J/kg MLCAPE air mass.
So will need to monitor and make sure this feature doesn`t cause any
mischief into the evening hours.

Ahead of the approaching cold front should be quite a bit of
convective activity expected to develop across the Midwest during
the late afternoon/evening hours.  Leading edge of what remains of
this convection may reach eastern Upper/far northwest Lower toward
daybreak Wednesday.  Cold front expected to push into eastern Upper
later Wednesday morning and into northern Lower during the
afternoon...with an axis of 1.75-2.00 inch precipitable water along
it.  Should be a corridor of heating ahead of the cold front which
is expected to gin up 1000-1500J/kg MLCAPE across northern Lower...
so precipitation chances should increase during the afternoon.  Like
today deep layer shear is forecast to be relatively minimal
(generally under 20kts 0-6km)...so organized severe potential is low
outside of some pulse-y severe storms that may gust out.

Continued hot and humid Wednesday: Looks like a warm night ahead
give humid air mass and southerly breeze which should persist.
Temperatures Wednesday will be dependent on cloud cover but will
have a head start with expected overnight lows mainly in the
70s.  Looks like there should be a corridor of good heating
ahead of the front across northern Lower...aided by southwest
downsloping into northeast Lower. Expecting areas along/east of
the I-75 corridor across northeast Lower should warm into the
90-95 degree range...heat indices in the mid 90s could push the
need for a Heat Advisory over northeast Lower but that is call
better made by the overnight shift.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 359 PM EDT Tue Jun 18 2024

PATTERN SYNOPSIS/FORECAST:

Anomalous longwave pattern across North America today...with
troughing over the western US into north central Canada...and strong
ridging building over the eastern US. Strong southwesterly flow
through the column...with upper jet over Canada around 140+kts, and
LLJ into the Upper Midwest running around 40-50kts, even after
nocturnal influences have diminished. Southwesterly warm advection
also aiding in plume of EMLs stretching from the southern Plains
well into MN (700mb temps in the low teens). Decaying activity north
of this continues to trek through Canada. Subtropical high over the
Carolinas resulting in excellent return flow up the MS Valley, with
pwats exceeding 1.5-2in. through that region. Pwats even bumping up
to 1.46in here in northern MI with our 12z sounding. PV max trekking
NNEward into SW MI early this afternoon with attendant shower
activity.

Looking ahead...expecting aforementioned PV niblet to zip through
today into tonight. Upstream PV (southern lobe of broader troughing)
over MT to jam its way up into MN going into Wednesday night and
Thursday as surface high pressure tries to settle in. However,
additional energy diving into the back of this helps shunt it out of
the region a bit quicker for the weekend...though there is still
some potential it could be a little more active. Aforementioned
surface high retrogrades into TN going into the end of the week,
with generally pleasant (albeit hot) conditions expected. A clipper-
type system approaches the area Saturday, though strength of this
feature is still somewhat nebulous, as there`s uncertainty in how
deep this feature will develop as it crosses the N. Plains. While
both ideas suggest it may not be entirely quiet this weekend
(naturally), there is some potential for a more tightly wound system
to cross into the area, which could be a little more active and a
little breezier. Otherwise...generally zonal flow in the presence of
the active storm track suggests we could have some potential for
multiple rounds of storms/rain tracking over similar broad areas
later in the week/weekend as well, which will be worth keeping an
eye on going forward. Perhaps some signals of relief finally arrive
on the horizon going into the start of next week, with troughiness
trying to return to the Great Lakes again.

Primary Forecast Concerns:

Heat continues...periods of relief at times...  Anomalous
subtropical ridge continues to hang on to our south, and as we`re on
the periphery of it with the BCZ so close...will expect things will
waver back and forth across the area through the period. Cold front
wavering south across the region on the southern flank of a stronger
push of energy will drag the boundary south into central Michigan
Wednesday night into Thursday and stall it out. Expect cooler and
somewhat drier air to filter in from the north in its wake, with
perhaps even a period of more seasonable weather over the northern
half of the CWA. Looks like the boundary pivots back north again on
return flow Thursday night into Friday, which should bring
heat/humidity back into the picture for the end of the week for us,
with highs again into the upper 80s and low 90s (barring any
convective debris that could keep things cooler)...with dewpoints up
into the 60s again. Generally stalled boundary looks to slowly slide
out going into Sunday, with a brief reprieve to more seasonable
temps in the 70s/low 80s with lower humidity...though an uptick is
possible early next week as another wave of energy approaches and
shunts the ridge axis overhead again. Some signals attm for a more
definitive cooldown for the end of the period, though not sure how
long it will last, given the pattern attm may be rather zonal
overall.

Storm chances continue...especially this weekend...  Current air
mass in the presence of an approaching boundary for Wednesday night
should help trigger some convection, and potentially through the
remainder of the period as it stagnates and meanders back and forth
over the area. Generally stagnant flow suggests little shear to
support organized storms, though stagnant flow could certainly
support the idea of at least slow-moving convection...which, in this
anomalously moist air mass, could be problematic from a heavy rain
standpoint...as it wouldn`t be impossible for a couple inches or
more of rain to fall over a single area...though confidence in this
exact area is low, given the nature of convection and the potential
mesoscale boundaries that could also enhance this threat.
Additionally, as another plume of anomalous moisture floods
northward into the region on warm advection Saturday...will
certainly have to keep an eye out as training convection is not
entirely out of the question...though even so, wherever the air mass
is able to get wrung out, it could certainly produce a lot of rain.
Especially if this boundary ends up being a bit slower to move
through the region.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 700 PM EDT Tue Jun 18 2024

Upstream cold front currently stretching thru the length of
Minnesota into the Central Plains will march eastward into the
Western Great Lakes region late tonight into Wednesday. Chances
of showers and storms will gradually increase on Wednesday along
and ahead of this front. Prevailing conditions will remain VFR...
but will temporarily drop to MVFR/IFR within any heavier showers
and storms that develop. Southerly surface winds at around 10 to
20 kts tonight will shift to the west and eventually NW on
Wednesday as this cold front sweeps thru our area.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT Wednesday for LMZ323-341-
     342-344>346.
     Small Craft Advisory until 8 PM EDT this evening for LSZ321.

&&

$$

SHORT TERM...JPB
LONG TERM...FEF
AVIATION...MLR