Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
729 PM EDT Sat Mar 28 2015
Short term...(this evening through sunday)
issued at 337 PM EDT Sat Mar 28 2015
Upper air pattern consists of a deep 500 mb trough over the eastern U.S.
This morning with a shortwave ridge across The Rockies and a
shortwave in the Pacific northwest. This ridge moves into the upper Great
Lakes tonight while the shortwave moves into the northern plains and
then the shortwave moves through the upper Great Lakes on sun.
NAM brings in some 850-500 mb q-vector convergence tonight with
deeper moisture coming in late tonight. The moisture starts to head
out late Sun afternoon with q-vector divergence moving in by sun
evening. GFS and European model (ecmwf) show about the same thing as well.
Quiet forecast for tonight as precipitation holds off until Sunday and then
forecast becomes complicated in a hurry. Will have very dry air
aloft to work through first and held off on the precipitation until 12z
Sunday over the west and increased probability of precipitation Sunday morning to
categorical. Looked at numerous soundings for mixed precipitation and looked
to ME like the majority of the precipitation would stay as snow especially
across the east half of the County Warning Area as wet bulb zero heights stay low
with plenty of evaporation to cool the soundings all below zero.
Even if there is some warm air aloft which the NAM is the most
aggressive with...feeling is that with the dry air tonight...would
cool this back below wet bulb zero.
The warm air tries to make it into the west in the afternoon...but
by that time...the deeper moisture is moving out and there could be
a rain/snow mix in the west in the afternoon. Over the east...the
precipitation will stay as all snow and could see a quick 3-6 inches of snow
over Schoolcraft and Luce counties and for that reason went with a
Winter Weather Advisory for them from late Sunday morning into
Sunday evening. Total quantitative precipitation forecast for this event looks to be from 0.20 to
0.35 inch with snow ratios fairly low in a wet and heavy snow. For
temperatures...did not make too many changes to the going forecast.
Used a non duirnal temperature curve for tonight with lows shortly
after midnight...then temperatures slowly warming and highs on Sunday will
be late in the day.
Long term...(sunday night through saturday)
issued at 403 PM EDT Sat Mar 28 2015
..active short term continues into the long term as well...
Active pattern expected through this week as bundle of shortwave
energy over the northern Pacific and Gulf of Alaska translates over
northern Continental U.S. And Great Lakes. May sneak some a couple warmer days
in as we begin April. Best chance for warmer days will be Wednesday and
Thursday. Along with this warmth will come strong winds as well.
Active pattern begins with tail end of system moving through on
Sunday. Widespread snow should taper off in the evening for far east
with lesser chances of precipitation elsewhere. Soundings indicate deeper
moisture departs while there is sufficient moisture at temperatures warmer
than -10c...so may see the precipitation try to diminish as dz or even light
rain. May see another inch of wet snow before the snow ends though.
Coordinate with the short term forecaster and decided that Winter Weather
Advisory will go through 11 PM on Sunday night to cover lingering
snow and sloppy mix of snow/drizzle. Kept higher probability of precipitation near Lake
Superior through the night...highest over the east along track of
another shortwave moving through and as this area is where 850 mb
thermal trough latches up with residual 850 mb- 700 mb moisture. Upslope
flow with northwest flow will drive the probability of precipitation elsewhere along Lake Superior.
Northwest winds could be pretty fierce on Sun night. Soundings indicate
cooling is not enough to turn the sounding to an unstable
profile...but given significant 3-6hr pressure rises to 10 mb
shifting west to east over the area and strength of winds just off
the deck...h95 winds over 40 kts and 850 mb winds over 50 kts...gusts to
advisory level seem possible along much of Lake Superior and especially
over the Keweenaw. Will mention in the hazardous weather outlook.
Generally quiet on Monday...though still breezy with lingering
gradient in wake of departing low pressure system. Since thermal
trough is in vicinity...low-level lapse rates over 8c/km on Monday may
allow for isolated-scatterd snow showers for the east half. Moisture
depth to around 850 mb may cut down on coverage/extent...but even so
carried small chances. Surface temperatures climb into the upper 30s or lower 40s
in the afternoon...so could even see rain mix in with the snow.
Expect next round of precipitation Monday night into Tuesday as clipper
type shortwave and associated low-level trough slide southeast
across upper Great Lakes region. Differences in models mainly in how
far east shortwave tracks as it digs southeast. This affects where
strongest lift occurs and also how much warm air gets pulled in just
ahead of the surface trough which eventually deepens into more closed
off surface low as it slides over WI. 12z NAM trended farther east while
12z GFS keeps with shortwave and heavier quantitative precipitation forecast staying mostly over
west to scntrl Upper Michigan. GFS idea similar to previous couple
runs and also to the 00z European model (ecmwf). 12z European model (ecmwf) and Gem-New Hampshire are very
shunted to the south and east...so models still all over the place
with the stripe of heavier quantitative precipitation forecast. Can not completely rule out NAM idea
as just 24 hour ago the models showed that far east of a track to the
system...but seems to be an outlier. Mixing ratios up to 2.5g/kg
into the system would point to 2-4 inches of snow in 6-9 hour
period...that is if precipitation falls as only snow. Soundings point to a
lot of lift occurring at temperatures warmer than -10c...suggesting a
wetter snow with slr/S around 10:1. As deeper moisture is stripped
out late Monday night into Tuesday morning...may see the precipitation try
to diminish and end as flurries/fzdz. NE winds on north side of surface
low would favor higher terrain of central Upper Michigan to see best
chance of precipitation during the day on Tuesday.
Weak surface ridge crosses western Great Lakes later Tuesday into
Tuesday night. Middle clouds increase on Wednesday ahead of next low
pressure system. Soundings show a lot of dry air even into Wednesday
afternoon...which will delay development of precipitation by Wednesday night.
Best chance of saturation appears over the east County Warning Area. Over the
west...the dry air may prohibit of much precipitation at all. Enough
warming in low-levels that whatever precipitation occurs would take the
form of rain. Since the surface low tracks just north of Lake Superior
into Thursday morning...1000-700mb dry slot sweeps over Upper Michigan
after midnight Wednesday night into Thursday morning. GFS farther
south with surface low compared to European model (ecmwf)/Gem-NH so it shows moisture
wrapping back over northern County Warning Area by Thursday afternoon in cyclonic flow.
Plenty of time to sort out these details...so will head toward
consensus at this point for Wednesday into Wednesday night. Given
strength of surface low and low-level jet and pressure falls moving over
and north of the area...expect strong winds. Thickening middle clouds
will cut down heating/mixing and stable low-level temperature profile also
will limit strength of winds making it to the surface. Will be a
balancing act between the stable profile and surface gradient. Will lean on
the blyr winds at this point...which would support south winds Wednesday
afternoon 20-30 miles per hour with higher gusts. Should stay windy into Wednesday night
and Thursday as the front moves through shifting winds to northwest
and bringing colder air into the area. Temperatures probably not cold
enough for much lake effect snow downstream of the open waters of Lake
Model divergence only increases Friday into next weekend. Case in
point is the 00z European model (ecmwf) indicating another shortwave working across
the plains comes far enough north while becoming negatively tilted
on Friday to bring a widespread wet heavy snow to much of the
forecast area. Quantitative precipitation forecast with that model run showed over an inch in some
areas. Consistency in that idea is low though as 12z/27 March run
looked a lot like latest GFS idea in showing a flatter wave and only
light quantitative precipitation forecast over upper Great Lakes. 12z European model (ecmwf) showed system coming in
slower and not as far north. Overall...given extent of upper level
energy and strong upper level jet plowing eastward late this week
cannot say a stronger system may not happen...but also cannot buy
off on this completely yet.
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 728 PM EDT Sat Mar 28 2015
As S winds increases tonight above a shallow inversion caused by nocturnal
cooling and under the tightening pressure gradient between surface hi pressure
moving toward the Middle Atlantic States/low pressure in scentral Canada
sliding southeast toward the upper lakes...expect low level wind shear to develop at all the
taf sites. With lingering low level dry air...VFR conditions will persist
despite incrsg hi clouds. As the low moves through Ontario on sun...some
mixed precipitation will overspread Upper Michigan. The best chance for accompanying lower
IFR conditions for at least a couple of hours will be at cmx and saw...
which will be closer to the sharper dynamic forcing associated with
the low. Iwd will also be impacted by a stronger downslope south-southwest wind
component that will lower the chance for IFR conditions. The onset of the
precipitation will cause the strong winds aloft to reach the surface...with wind
gusts as hi as 25-30kts. Look for the precipitation to diminish by middle/late
afternoon with the arrival of larger scale subsidence and the passage of
a cold fnt...allowing conditions to improve. But gusty west-northwest winds will
also follow the frontal passage. The uslope nature of these strong winds at
cmx will slow the imrovement at that site...with IFR ceilings lingering
there through the end of the taf period.
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 337 PM EDT Sat Mar 28 2015
Strong southwest winds expected late tonight through Sunday night as
low pressure system crosses Manitoba and northern Ontario. Southwest
gales possible with this system on sun...especially on the east
half. Northwest gales possible Sunday night into Monday in wake of
the low pressure system and trough. Series of low pressure troughs
Cross Lake Superior through the rest of next week...but winds are
expected to stay mainly below 20 kts.
Winter Weather Advisory from 11 am to 11 PM EDT Sunday for
Gale Warning from 8 am Sunday to 5 am EDT Monday for lsz249>251-
Gale Warning from 2 am EDT /1 am CDT/ to 11 am EDT /10 am CDT/
Sunday for lsz162-263.
Gale Warning from 2 am to 8 PM EDT Sunday for lmz221-248-250.