Bill Schintler
EF4
The last of a series of progressive clipper systems will affect the upper Midwest Sunday afternoon. The heaviest accumulations will be to our north, with most locations in east central Iowa receiving less then a half-inch of snow and with snowfall ending by late afternoon. Some light freezing drizzle will be possible south of US-30 during the evening hours. Attention then turns to a much more significant system that will bring freezing rain and significant snow accumulations to the area on Tuesday and Wednesday. Below are forecasts for specific locations in eastern IA for Sunday:
Cedar Rapids (Easter Iowa Airport)
Light snow will start at 11:30 AM and accumulate to between a dusting and 0.5 inches.
Iowa City:
Light snow will start at 11:45 AM and accumulate to a dusting.
North Linn Co. (Paris and Coggon):
Light snow will start at 11:15 AM and accumulate to 0.7 inches.
Marengo:
Light snow will begin at 11:30 AM and accumulate to between a dusting and 0.5 inches.
Discussion:
Upstream 00Z soundings (OAX, ABR, and BIS) indicate a dry AMS over modest moisture below H8. SFC obs indicate that precipitation is reaching the ground in WRN ND. Models appear to have a good handle on 00Z H925-H7 moisture and temperature profiles as well as QPF. The UA pattern over the CONUS is advertised to undergo significant changes over the next 72 hours. The persistent Hudson Bay/Great Lakes low finally shifts NE while a piece of energy now entering the PAC NW really starts to dive S while phasing with an ULVL low off the coast of CA. A transition to a split flow ensues, with the SRN branch rapidly amplifying into a deep trough over the SWRN states through day-3. The current snow depth chart shows snow cover extending S to nearly I-70 in MO. This snow pack will reinforce the cold AMS to our north and the baroclinic zone to the S. This gradient should serve to intensify the Tuesday-Wednesday storm with attendant strong moisture advection. Models do not yet appear to have a good handle on neither this nor the evolution of the ULVL jet.
On Sunday, CI will overspread the area by daybreak, and mid-level WAA clouds will reach the I-380 corridor at 14:30Z with rapid column saturation through 17Z. FCST SFC/H85 temperatures range from 17F/-8C early in the event and rise to around 23F/-4C at the end of accumulating precipitation. Accordingly, the snow/liquid ratio is tapered from 14:1 down to 12:1. An H7 omega bulls-eye of -10ub/s quickly translates through ERN IA along US-20 between 18Z and 21Z, with weak subsidence in its wake. Therefore, expect 3-hour event duration with PWATs averaging 0.4 inches and a dendrite growth zone between 30 and 40mb. Bufkit soundings have consistently indicated snowfall amounts of less then a half inch in ECNTRL IA.
- bill
KD0DJG
10:00 PM CST, 12/06/08
Cedar Rapids (Easter Iowa Airport)
Light snow will start at 11:30 AM and accumulate to between a dusting and 0.5 inches.
Iowa City:
Light snow will start at 11:45 AM and accumulate to a dusting.
North Linn Co. (Paris and Coggon):
Light snow will start at 11:15 AM and accumulate to 0.7 inches.
Marengo:
Light snow will begin at 11:30 AM and accumulate to between a dusting and 0.5 inches.
Discussion:
Upstream 00Z soundings (OAX, ABR, and BIS) indicate a dry AMS over modest moisture below H8. SFC obs indicate that precipitation is reaching the ground in WRN ND. Models appear to have a good handle on 00Z H925-H7 moisture and temperature profiles as well as QPF. The UA pattern over the CONUS is advertised to undergo significant changes over the next 72 hours. The persistent Hudson Bay/Great Lakes low finally shifts NE while a piece of energy now entering the PAC NW really starts to dive S while phasing with an ULVL low off the coast of CA. A transition to a split flow ensues, with the SRN branch rapidly amplifying into a deep trough over the SWRN states through day-3. The current snow depth chart shows snow cover extending S to nearly I-70 in MO. This snow pack will reinforce the cold AMS to our north and the baroclinic zone to the S. This gradient should serve to intensify the Tuesday-Wednesday storm with attendant strong moisture advection. Models do not yet appear to have a good handle on neither this nor the evolution of the ULVL jet.
On Sunday, CI will overspread the area by daybreak, and mid-level WAA clouds will reach the I-380 corridor at 14:30Z with rapid column saturation through 17Z. FCST SFC/H85 temperatures range from 17F/-8C early in the event and rise to around 23F/-4C at the end of accumulating precipitation. Accordingly, the snow/liquid ratio is tapered from 14:1 down to 12:1. An H7 omega bulls-eye of -10ub/s quickly translates through ERN IA along US-20 between 18Z and 21Z, with weak subsidence in its wake. Therefore, expect 3-hour event duration with PWATs averaging 0.4 inches and a dendrite growth zone between 30 and 40mb. Bufkit soundings have consistently indicated snowfall amounts of less then a half inch in ECNTRL IA.
- bill
KD0DJG
10:00 PM CST, 12/06/08
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