Category Archives: Winter Weather

Winter Weather

WINTER WEATHER UPDATE- TUES 9:40 PM

The latest NAM data has become available.  According to the NAM, the snow starts between 9 and 11 AM.  Total QPF falling as snow  varies by location, but in and around the city, about 0.30 inches water or about 3 inches of snow before mixing with sleet and freezing rain.

North and west of the city, QPF values falling as snow increase to about 0. 40 inches water, with an additional delay in the changeover.   About 4-5 inches possible in areas north and west of the city.

Because it’s already the third week of February,  the sun angle is high; solar insolation through clouds may reduce accumulation on dark pavement and roadways.

The changeover to sleet is expected between 4:30 and 6 PM.  An hour or two of sleet and freezing rain before changing to rain.

Most of the heavy precipitation will fall as rain, leaving a soggy mess by morning.  Temperatures are expected to stay above freezing towards morning, so additional freezing of fallen precip is not expected with this storm.

These sort of warm air over-running cold air scenarios  with cold air damming are tough to predict accurately.  Let’s see how it unfolds.

Winter Weather

WINTER WEATHER UPDATE -MON 6 PM

[su_box title=”Winter Weather Update: Monday Evening ” box_color=”#defcdc” title_color=”#000000″]Tonight’s NAM has become available. The NAM has snow starting about 9-10 AM Wednesday and continues as snow until 4-6 pm, when it starts mixing and changing to all sleet by 7pm. Temperatures remain at or below freezing until early evening.

Based on QPF, 4-6 inches of snow may accumulate before the changeover. A further changeover to rain will occur later in the evening. Heavier rain about midnight.

This is a preliminary forecast. Expect changes with future model runs.  [/su_box]

From earlier..

Here’s the latest on the snow that’s expected for Wednesday.  As usual, there’s a fair amount of model disagreement.

This morning’s GFS had the snow starting as late as noon, however this morning’s run of the new FV3-GFS had the snow starting about 8 AM.   This afternoon’s high resolution NAM NEST has the snow starting about 10 AM.

This will be a storm where the total QPF will be divided into snow, sleet and rain components.  Most of the models are in general agreement that there will be about 3-6 inches of snow, with a lean towards the lower end, before a changeover to sleet and then eventually to rain.  BTW, the European (ECMWF) has 4-6 inches for our area.

Models have the changeover from snow to sleet anytime from 3PM to 7 PM.   Sleet will likely fall for several hours as it mixes with rain. The heaviest precip will occur as rain towards midnight and after.

As discussed earlier, this will be another “warm air aloft over-runnng cold air at the surface” type system, actually a warm frontal-type system.

The forecast accuracy for this type of system has little to do with the “track of the storm” as they say on TV, but rather with the three dimensional thermal profile of the atmosphere and the eventual placement of the moisture plumes and dynamics.   There’s no storm center “to track” here; it’s more subtle than that.

Getting the forecast even close to correct probably won’t be possible until Tuesday night’s model runs.