National Weather Service - Area Forecast Discussion
000
FXUS63 KAPX 260207
AFDAPX
Area Forecast Discussion
National Weather Service Gaylord MI
1007 PM EDT Thu Apr 25 2024
.KEY MESSAGES...
-- Elevated fire danger Friday afternoon.
-- Increasing confidence in rounds of showers and thunderstorms
impacting northern Michigan from Friday night through Monday.
-- Chance for severe thunderstorms, particularly later Saturday
into Saturday night across northern lower Michigan.
&&
.UPDATE...
Issued at 1007 PM EDT Thu Apr 25 2024
All is quiet across our Northwoods late this evening...with
high pressure...strong subsidence and dry air overhead. Little
will change overnight...with clear skies and light SE winds
expected. Overnight lows will cool into the upper 20s and lower
30s.
&&
.SHORT TERM /THROUGH SATURDAY/...
High pressure still focused just to our east over Ontario...with PV
maxima dropping across the CWA attm. Light and variable winds with
lake breeze development today...and seeing a very few cu pop up over
NE Lower, where some upsloping may be aiding in lift and saturation,
combined with some slight moisture advection off the lake as that
weak bit of PV moves through.
Expecting high pressure to remain over the area tonight...though
return flow should rotate into the region going into Friday morning,
and especially Friday afternoon, with increasing warmth aloft, as
well as an increase in overall moisture. However...southeast flow
hangs on into Friday as well, and antecedent dry air mass should
preclude most, if not all, precip from reaching the ground over the
region till beyond this period.
Primary Forecast Concerns:
Increasingly warm and breezy, remaining dry...Expecting temps aloft
to increase through the day Friday, and with mixing up to around
850mb, think highs in the upper 50s to lower 60s are quite probable,
especially considering we should remain largely clear...and temps
will not fall as much tonight as they did last night. With better
downsloping over NW Lower...think some upper 60s could be possible
as well...though I do have to admit that we should start to get
better mid/high cloud coverage into that area with time in the
afternoon. Current dry air mass will take time to saturate...and
suspect this may hold off even some of the cloud cover until later
in the afternoon/evening; even less can be said for precip, which
should hold off till Friday night and beyond. Some suggestion that
another lobe of lower dewpoints could pivot over the region from
north to south Friday, which could allow for afternoon RHs to fall
even further below the usual 25 percent criteria for fire weather
thresholds. Have not gone quite this aggressive, but have elected to
keep dewpoints (and subsequently, RHs) a touch lower even so.
Additional concerns for fire weather as pressure gradient begins to
strengthen with system tracking across the Plains; expecting 5-10kts
sustained winds, which could gust as high as 20-25kts by evening.
Admittedly, this is more of a warm advection setup for winds, which
typically would not be as favorable for gustiness...though do think
the antecedent dry air mass and good potential for mixing could aid
in better gusts this time around...at least, while the sun is
out.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Pattern Synopsis / Forecast: Active baroclinic zone will really get
its act together over the course of the weekend as a complex setup
of shortwaves and associated surface low pressure centers / frontal
boundaries pass through the upper Great Lakes region, dispatching
the dry influences of surface high pressure progged to be moving off
the Atlantic coast of New England. The action begins Friday night as
a surface warm front moves into the region, bringing a round of
showers and potentially some thunder too. The next car in the
metaphorical atmospheric train will be surface low pressure
advancing east from Wisconsin into the U.P., drawing in a warmer and
potentially much more unstable airmass before a surface cold frontal
boundary moves into the region and sparks off another chance for
showers and storms late Saturday, some of which could be strong to
severe. This frontal boundary largely becomes stationary over the
region by Sunday, continuing unsettled weather potential Sunday into
Monday as yet another low pressure center works into the Great
Lakes. The passage of this low pressure center should mark the end
of the active stretch of weather, with surface high pressure progged
to intrude into the Great Lakes as we move closer to midweek.
Primary Forecast Concerns:
Friday Night Convection: Despite warm / moist advection moving into
the region, there will be some barriers to overcome as we progress
into the overnight hours. Stout low level dry layer will impede the
initial advances of a stratiform rain plume well ahead of the
surface warm frontal boundary. It wouldn`t be overly surprising for
this plume to pass through the region with more of a whimper
considering progged soundings display dewpoint depressions as high
as 30 Celsius across the southwest part of the CWA around 00z
Saturday. The most appreciable rainfall from this frontal passage
will come later in the overnight when steepening lapse rates aloft
(up to 7 Celsius / km) and 850mb warm advection drive elevated
instability associated with the warm front. In theory, would like to
see steeper lapse rates to drive instability up for better thunder
coverage, but the moistening airmass should provide better rainfall
potential for places that see repeated shower passages Friday night
regardless. While instability is low (generally 100-400 J/kg),
suppose an embedded rumble of thunder or two cannot be ruled out.
Overall, looks like most spots probably see a general 0.25" or less
Friday night, though localized areas that see repeated downpours
could observe 0.75"+. At this time, severe weather potential looks
quite low Friday night into Saturday morning.
Saturday - Saturday Night: Uncertainty begins to riddle the forecast
as we progress into Saturday, particularly with respect to the
position of the surface warm frontal boundary. Most guidance has the
surface warm front clearing the Straits and stalling out somewhere
between the Bridge and the Soo, but there is a modest amount of
guidance that has the front stalling out around the M-32 area. The
former solution would generate more clearing / destabilization
potential amid warmer temperatures across northern lower into the
day Saturday, possibly as high as the upper 70s for some, while the
latter solution brings about a cloudier and cooler solution (upper
50s and lower 60s) with a stable layer in the low levels and thus
suppresses the majority of surface based convection to the south and
west. Considering favorable low pressure position based off severe
climo for northern Michigan and the 500mb ridge axis located just to
our east, this in theory should allow for an easier warm frontal
passage, despite the suppressing efforts of the colder Great Lakes.
In the event that this solution pans out, this opens a Pandora`s Box
of convective potential across the region.
Being in the vicinity of the triple point of the system will lead to
favorable dynamics aloft to contribute to severe weather potential
later Saturday into Saturday night as the surface low and associated
cold front move into the region. Bulk shear increases considerably
with the intrusion of the triple point (as high as 40-50kts). In
addition, SRH values balloon above 200 m^2/s^2, indicating ample
potential for rotating updrafts to materialize with any surface
based storm that initiates. The final thing that will need to come
together will be the maintenance of surface / low level moisture.
Guidance wants to keep dewpoints well into the 50s and even into the
lower 60s, which would lower cloud bases and bypass the potential
suppressing nature of warmer air aloft in the profile. If we can
achieve the higher end of this dewpoint range, coupled with the
other aforementioned favorable dynamics, this could lead to all
hazards being on the table Saturday evening / early overnight, with
heavy emphasis on wind and hail (non-zero chance for these hazards
to be locally significant if a more discrete / supercellular storm
mode can be realized). Tornadic activity will be somewhat
questionable owing to shear vectors being more parallel to the cold
front as opposed to normal to the boundary as it approaches northern
Michigan (thus leading to the eventual stationary nature of the
front), but risk still remains non-zero. Additionally, the parallel
relationship of shear vectors and frontal orientation could set up a
heavy rain sequence with any potential training thunderstorms as
PWATs swell to 1.00-1.25 (200-300% of climo normal).
This setup has a very low floor, but a high ceiling that can`t be
overlooked despite ongoing forecast uncertainty. This is reflected
by SPC already electing to place northern lower Michigan within the
Day 3 Slight Risk (level 2/5) for the conditional threat of severe
weather. Numerous more updates are to be had in the coming forecast
cycles as details on the evolution of this sequence become clearer.
Rest of the Period: The cold front will stall out overhead and
become stationary by Sunday, and with additional disturbances
expected to ride this area of forcing, this spells additional rounds
of showers and storms at times Sunday into Monday, bringing
additional rainfall. Eventually, low pressure will pass through the
region and the stalled front will be forced eastward by intruding
high pressure. By Tuesday, conditions look to be drier but still on
the mild side, with highs in the upper 50s to upper 60s and lows
generally in the 40s. One final note- considering that we will be
dealing with warm daytime temperatures and mild nights coupled with
mild temperatures accompanying rainfall, this should spell the
arrival of spring greenup in the next week or so, particularly
across northern lower Michigan. This could open the door for any
frost / freeze impacts beyond the forecast period to be
amplified.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Large area of strong high pressure will currently centered over
the Great Lakes region will slowly push eastward into New
England over the next 24 hours. Skies will remain clear tonight
into Friday...but will begin to increase by Friday night as
moisture begins to surge northward well in advance of a
developing storm system over the Central Plains. Solid VFR
conditions are expected at all Eastern Upper and Northern Lower
Michigan TAF sites thru early Friday evening. Light SE winds
tonight will strengthen to 15 to 25 kts on Friday.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
UPDATE...MLR
SHORT TERM...FEF
LONG TERM...HAD
AVIATION...MLR
NWS APX Office Area Forecast Discussion
