Debate de meteorólogos científicos
Area forecast discussion
National Weather Service Marquette Michigan
424 am EST Friday Dec 13 2013
issued at 942 PM EST Thursday Dec 12 2013
Main forecast concern this evening has been on timing/impact of intense les
band shown on MQT 88d over scentral lake supply extending into far eastern
Alger/northern Luce counties. This band has been nearly stationary through much
of the evening...with hiest reflectivities aprchg 30 dbz as hi as 6-7k
feet...prompting issuance of an Special Weather Statement earlier in the evening. Call to
spotter just S of Grand Marais indicated snow falling at the rate of
an inch/hour with total accumulation from noon through 9 PM around 7 inches.
The band intensified during the evening with sharpening low level cnvgc
accompanying more pronounced land breeze SW wind component on the
southern flank of the band. Considered upgrading advisory to warning to this
area...but recent radar imagery indicates the band is beginning to
shift to the S in line with veering low level winds to the northwest...which is
in agreement with higher res model forecasts. In fact...nearby surface observation/mqd
88d vwp do show a veering trend. With the steady veering expected
through the night and forecast weakening land breeze cnvgc...expect the band
to move more steadily and diminish a bit with time. With weaker
multiple banded les expected to dominate...will hold on to going advisory
for Alger/Luce/nrn Schoolcraft counties.
Otherwise...tended to bump up min temperatures forecast a few degrees with quite a
bit of cloud cover and wind shift to a more north direction allowing for More
Lake supply moderation.
Short term...(this evening through friday)
issued at 419 PM EST Thursday Dec 12 2013
WV imagery and RUC analysis indicated a broad middle/upper level trough
across eastern noam resulting in northwest flow through the northern Great Lakes. A
shortwave trough was moving through northwest Ontario dragging a cold front
through Western Lake Superior. Farther upstream...a weak clipper shortwave
was moving from southern Saskatchewan into the northern plains. Les bands aligned with
west-northwest flow through Eastern Lake Superior into NE Alger and northern Luce
counties had diminished slightly and become more cellular this
afternoon with weakening low level conv from land breeze component.
Expect that the low level winds will diminish and veer from west-northwest to
nearly. This should push the more significant les through much of the
eastern County Warning Area from Alger County eastward as a strengthening land breeze
should keep most of the snow east of Marquette. Even with the
shifting position of the les bands...favorable snow growth with the
dgz in the 1k-4k convective layer pushing slr values above 25/1 and
should support advisory snowfall amounts in the 3 to 6 inch range.
Over the west...the shorter fetch...anti-cyclonic flow and lower inversion
heights from 3k-4k feet...will keep snowfall amounts in the 1 to 3
From late tonight into early Friday...the Saskatchewan shortwave and weak upper
level divergence with the right entrance of a 140 knots 250-300 mb jet with
associated 800-600 mb fgen may support a band of light snow.
However...models suggest that the best chance of light snow with
these features will remain over WI. So...only chance probability of precipitation with
accumulations less than a half inch were included.
Winds will continue to veer Friday as Arctic high pressure from
Saskatchewan/Manitoba into northern Ontario builds into the northern lakes. With winds
shifting from north to north-northeast the most favorable low level conv will shift
from the NE County Warning Area into Marquette County. While snow growth will remain
favorable...inversion height remaining near 5k-6k feet with mainly
anti-cyclonic upstream flow may limit les intensity and snowfall amounts
below advisory levels. Generally 1 to 3 inches are expected with the
greatest amounts in far western Alger County into eastern Marquette County.
Long term...(saturday through thursday)
issued at 423 am EST Friday Dec 13 2013
NAM shows a 500 mb ridge over the western U.S. 12z Sat with a
shortwave trough over the central U.S. A closed 500 mb low over
northern Manitoba digs southeast on Sat and digs a deeper trough
into the upper Great Lakes which affects the area late on Sat into
Sat night. This trough moves into the lower Great Lakes on sun.
NAM shows some 850-500 mb q-vector convergence and some deeper
moisture Sat night and both leave on sun. Looks like there could be
some lake enhancement with east flow going on over the Keweenaw and
also from Lake Michigan across Menominee and Delta counties on
Saturday with a dry wedge of air in between over the central and
eastern County Warning Area in the morning and tried to reflect the two areas of
precipitation in the probability of precipitation grids. Will go categorical with the lake
enhancement over southern Menominee and across the northern Keweenaw
peninsula as lake temperatures are around 4c and GFS and NAM are
showing 850 mb temperatures of -16c to -20c. These areas might need
advisories for lake enhanced snowfall as there could be 4-6 inches
of snow Sat and Sat night with this next system. Will let day shift
look at this possibility again...but right now looks like advisory
snowfall. This dry air erodes in the afternoon and went chance probability of precipitation
across the central and east then. Lake effect starts Sat night
across the west in Northwest Lake effect snow belts and this
continues into Sunday evening. Did not make too many adjustments to
going temperatures except to lower low temperatures a bit more
during the nights with lighter winds.
In the extended...GFS and European model (ecmwf) show a broad 500 mb trough across
the U.S. 12z Monday. This broad trough remains 12z Tuesday with a stronger
shortwave digging into the upper Great Lakes. This trough moves into
the eastern U.S. 12z Wednesday. European model (ecmwf) then shows a strong trough digging
into The Rockies 12z Thursday while the GFS is zonal with its upper flow
and solution is totally different. The GFS has a high pressure
system over the Great Lakes 12z Thursday. Looking at the manual
forecasts...looks like the European model (ecmwf) solution was followed on Thursday. Still
looks colder than normal this forecast period. Will have chance probability of precipitation
in for Monday with passage of a shortwave across the area and then
Monday night there could be some lake enhancement over the eastern County Warning Area
off of Lake Michigan and went likely probability of precipitation there with chance probability of precipitation
elsewhere. For Tuesday...Lake effect snow off of Lake Superior starts up
and went chance probability of precipitation for then and then the next system comes in for
Thursday and went chance probability of precipitation then.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1229 am EST Friday Dec 13 2013
Cmx...expect IFR visibilities with falling snow/blsn in gusty northwest flow early
in the forecast period to give way to MVFR conditions as the flow
weakens and veers to a more unfvrbl north-northeast direction.
Iwd...as the flow veers toward an upslope north and NE direction...
expect lake effect -shsn to increases at iwd early this morning. So MVFR
conditions early in the taf period should deteriorate to IFR by
sunrise. As the low level winds veer further to a more unfvrbl NE then east
direction Friday aftn/evng...conditions are likely to improve to MVFR
and perhaps VFR by evening.
Saw...expect VFR conditions early this morning to deteriorate to MVFR
by sunrise as the flow veers toward the north following a low pressure trough
passage. With a continued veering to an upslope north-northeast direction this
afternoon...visibilities are likely to fall to IFR with more frequent enhanced
shsn. As the flow veers further later this evening toward a less favorable
east direction...conditions will rebound to MVFR.
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 419 PM EST Thursday Dec 12 2013
A period of west-northwest to northwest gales is expected late this afternoon through
this evening before diminishing overnight with high pressure building
toward the region. Heavy freezing spray will also continue for much
of the lake into this evening. Winds will finally diminish to
northerly at 15 to 25 knots overnight into Friday morning as a weak
ridge passes across the lake. Expect 10 to 20 knots winds to gradually
back to the southeast by Saturday ahead of developing low pressure over the
upper MS valley. Depending on the strength of the low as it moves
across Lake Superior on Saturday night and Sunday and the strength of
another low moving up the East Coast...could see an increase in
northwesterly winds on Sunday to 25 to 30 kts. This will be short-
lived as another high slides into the area for the beginning of the
upcoming work week.
lake effect Snow Advisory until 6 PM EST this evening for miz006.
Lake effect Snow Advisory until 6 am EST early this morning for
heavy freezing spray warning until 7 am EST this morning for