National Weather Service - Area Forecast Discussion

FXUS63 KAPX 221335

Area Forecast Discussion
National Weather Service Gaylord MI
935 AM EDT Thu Apr 22 2021

Issued at 935 AM EDT Thu Apr 22 2021

Morning analysis reveals upper level trough axis extending from
Quebec down through New England with short-wave ridging building
through the Upper Midwest. N-S oriented compact upper jet
max is diving into the northern lakes with associated tail-end of
an upper vorticity max clipping the N/E part of the CWA. Just
enough background forcing...coupled with some lake contribution...
to kick off some light snow showers earlier in the morning and
create slick spots.

At the surface, sprawling high pressure is situated over the
lower Mississippi River Valley with subtle ridging extending up
through the western Great Lakes. A fair amount of dry air
encompasses the Great Lakes with PWAT values at or below one
quarter of an inch. So other than our nuisance cloud cover (and
earlier showers) there is a good amount of clear skies upstream.

First off, most locations under the freeze warning are already at
or above freezing. So...we`ve gone ahead and cancelled the freeze
warning a little ahead of schedule.

Meanwhile, tail-end of vorticity max will slide down through the
central Great Lakes through the afternoon with short-wave ridging
building into the western Great Lakes later in the afternoon
through tonight. Associated Precip appears to be about done with,
but there will be some associated cloud cover sliding down through
mainly the eastern part of the region over the next several hours.
Otherwise, given the degree of dry air across the region, warming
aloft and daytime heating/mixing, most areas will end up with a
good amount of sunshine.


.NEAR TERM...(Today through Tonight)
Issued at 340 AM EDT Thu Apr 22 2021

Impactful weather: Minimal/none.

Pattern synopsis and forecast:

Upper level troughing was moving into the eastern states early this
morning, with ridging working into the nrn Plains and Central
Canada. A weak shortwave with minimal forcing on the backside of the
troughing was crossing nrn Michigan, while CU debris/convection from
WI yesterday evening continues to work eastward across nrn lower
Michigan. This is likely aided is some fashion by still cold enough
lower level temperatures for overlake instability and subsequent
moisture flux off the Great Lakes. Otherwise, low level temperatures
were moderating, with low to mid level warm advection on the rise,
ahead of the upstream upper ridging.

The weak shortwave exits this morning, while the upstream ridging
marches eastward, settling over nrn Michigan by daybreak Friday. The
current convective debris/snow showers are expected to decay this
morning, probably in some degree by pressing further away from Lake
Michigan. The weather becomes pretty quiet, with just maybe a few to
scattered high-based cumulus over NE lower, and some increased high
level cloud spilling in via northerly upper level winds ahead of the
approaching ridging. Skies will be decreasing in cloudiness by
evening, with clear/mostly clear skies for most of tonight. The
entire time, low to mid level temperatures continue to warm, and we
start breaking this recent cold snap.

High temperatures will mostly be 45F to 50F, with some lower 50s in
downsloping areas in the far SE CWA. Lows will mostly be in the low
to mid 30s with upper 30s across much of the GTV Bay region/coastal
counties of Lake Michigan. Thus, do not think another freeze warning
for agriculture interests there will be needed.


.SHORT TERM...(Friday through Saturday Night)
Issued at 340 AM EDT Thu Apr 22 2021

High Impact Weather Potential: Low for now

Pattern Synopsis:

An amplified trough will continue to work its way off the Atlantic
coast as temporary ridging slides overhead on Friday. Subsidence
aloft behind this trough will build surface high pressure across
most of the eastern CONUS heading into the weekend. Two separate
shortwaves are expected to progress across the Midwest and far SE
CONUS Saturday, providing favorable ascent aloft to support
cyclogenesis/surface pressure falls across these respective regions.


Friday will be a pleasant spring day for most of the CWA, especially
when compared to the first half of this week. Highs look to reach
into the 50s with low 60s across NE lower underneath partly cloudy
skies during the afternoon. A very dry low-level airmass will be in
place which will keep the first half of the period precip-free. The
main focus will be Saturday when the next rain chances - and
potentially some more flakes of snow (...sigh...) - arrive,
beginning in the early AM hours. Support aloft provided by the
aforementioned shortwave will help spark some showers along somewhat
nebulous surface convergence - call it an ill-defined, elongated
surface trough, or even a sad warm front if you`d like - that looks
to stretch from SW to NE across a chunk of northern lower. The best
chance for Saturday AM showers is expected to be along this subtle
forcing across the southern half of the CWA, especially with closer
proximity to Saginaw Bay. Additional chances will exist across
eastern upper where these respective showers may last into the late
morning/early afternoon.

A second round of precip is expected to initiate along and ahead of
an approaching cold front moving in from Wisconsin Saturday
afternoon/evening. These rain showers are expected to initiate
across far NW lower and migrate eastward across the area with time
Saturday evening. Once again, rain showers will also be possible
across eastern upper behind the front. Some heavier downpours may be
possible with the presence of non-zero instability confined to the
low/mid levels despite cool surface temperatures. As the low-level
profile cools rather quickly heading into Saturday night with cold
advection behind the front and the cessation of diurnal heating,
snowflakes may mix in with ongoing precip. Additionally, light lake
effect snow can`t be ruled out as NW winds spread across the area
the further we go into Saturday night despite marginal conditions to
support it. As this week has shown, you can`t underestimate the
Great Lakes` willpower to generate nuisance snow - especially this
late in April. It just does not want to let go of winter, unlike
most of us around here that are ready for a real spring.

.LONG TERM...(Sunday through Wednesday)
Issued at 340 AM EDT Thu Apr 22 2021

High Impact Weather Potential: Monitoring the middle of next week
for active weather.

The aforementioned shortwave should quickly progress east of the
Great Lakes on Sunday as amplified upper-level ridging takes ahold
of the eastern CONUS at the start of next week. Southerly low-level
winds on the backside of dominant surface high pressure centered
over the Atlantic coast will advect a warm, moist - and essentially
summer-like - airmass northward all the way into the Great Lakes by
Tuesday. Highs in the 70s are expected across northern lower Tuesday
afternoon, which would be around 15 degrees warmer than normal for
the end of April.

The main focus of the long term will be the return of a more active
pattern to round out the month. Highly amplified troughing is
expected to gradually slide across the center of the country through
the middle of next week, providing support aloft for systems to trek
across the Plains and into the Great Lakes region. While specifics
regarding feature placement and strength are very murky, enough
confidence exists in deterministic and ensemble guidance to take
note of this period ahead. Current confidence lies in a less
progressive pattern than some model depictions (ECMWF) through the
middle of next week as guidance typically struggles to handle
strong, amplified ridging correctly - specifically how long they
stay put. That being said, belief is that the pattern will feature
more meridional flow through the troposphere with increasingly
amplifying upper-level features and, when combined with an airmass
that may push climatological max PWAT values, could be an early
signal towards heavy rainfall potential for the Great Lakes during
the middle/end of next week.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 540 AM EDT Thu Apr 22 2021

...VFR the entire TAF period...

High pressure will drift across the lower Mississippi valley and
toward the mid Atlantic/SE states tonight. A sfc ridge axis will
drive through nrn Michigan, shifting westerly winds more SW late
today and tonight, with some minor gustiness expected this
afternoon. FEW-SCT high based cumulus expected today at APN with
added high level cloud at all airports. The cumulus and higher cloud
fade this evening with skies becoming clear/mostly clear.


Issued at 340 AM EDT Thu Apr 22 2021

High pressure will drift across the lower Mississippi valley and
toward the mid Atlantic/SE states tonight. A sfc ridge axis will
drive through nrn Michigan, shifting westerly winds more SW today
and tonight. Low end advisory gusts are expected this afternoon for
far nrn Lakes Michigan and Huron, and possibly again Friday
afternoon in the same areas. Afternoon lake breezes/onshore flow
expected today and tomorrow on Whitefish Bay and for the nearshore
waters south of Alpena.


LH...SMALL CRAFT ADVISORY until 7 PM EDT this evening for LHZ345>347.
LM...SMALL CRAFT ADVISORY until 7 PM EDT this evening for LMZ341-342.



NWS APX Office Area Forecast Discussion