Forecast Updated Sat 10:44 AM — Clouds are moving in as forecast and the high resolution models have it cloudy Saturday afternoon with widely scattered snow flurries possible.
The models continue with delaying the precipitation on Monday into later in the morning, reducing the effects of any snow at the start.
The models didn’t do that well with Friday’s forecast; the light snow, freezing rain and sleet today lasted much longer than any models had predicted last night. I’m glad I sat this one out
Hopefully the models will do better this weekend.
For Saturday, an upper trough swings through with some areas of vorticity along with some moisture. Saturday starts sunny, but becomes cloudy around noontime. There’s a chance of snow flurries in the afternoon. High temperature 31.3° sd 1.3° (NBM Blue Bell).
For Sunday, high pressure finally builds in with mostly sunny skies. High temperature 34.6° sd 1.6° (NBM Blue Bell). The increasingly higher sun angle on Sunday will allow for considerable melting despite the low temperatures.
The next system to affect us will be on Monday. The model trend has been for precipitation to move in later, about mid to late morning. A later start will allow temperatures to rise more before the onset. Today’s models were predicting as much as 1-1.5 inches northwest of the city before a changeover to sleet, quickly followed by rain. I’m sure that will change, likely to less accumulation.
Some above seasonable temperatures Tuesday and Wednesday.
Sat 09:14 AM Update — This morning’s HRRR continues to show an area of clouds moving in later in the morning today associated with the vorticity—
• Some sun early, then considerable cloudiness in the late morning. Then, a mix of sun and clouds in the afternoon. • Some snow flurries possible early evening • High temperature 32.1º sd 0.9º (NBM model) Blue Bell. • Windy, especially mid-day. Winds 15 mph with higher gusts to 35.\
The potential snowfall for Monday night into Tuesday continues to look like a minor event. The NBM (model blend) picks up the trend with totals of 1-2 inches of snow by 7 AM Tuesday. (It pretty much ends by 7-9 AM. ) A mix of sleet and freezing rain at some points in the event will limit totals, although there isn’t all that much moisture with this storm to begin with.
NBM precip categorical type at 7 AM Tuesday. (Not to be confused with actual snow falling at the time- it’s NOT a radar image .) (Click on image for a larger view.)
Check back for updates later tonight.
From Friday evening…
Cold high pressure builds in for Saturday and Sunday. Ordinarily that means sunny skies, but an area of vorticity, moisture and cyclonic flow in the upper atmosphere will cause considerable instability cloudiness during the earlier part of the day Saturday—
SREF model showing area of vorticity (lilac) moving through. (Click on image for a larger view.)
(Note – continuing downtime of the main NOAA weather model distribution server has made some model data unavailable today.)
Saturday — • Sun early, then considerable cloudiness in the late morning. A mix of sun and clouds in the afternoon. • High temperature 31.9º sd 1.1º (NBM model) Blue Bell. • Windy, especially mid-day. Winds 15 mph with higher gusts to 30.
The upper flow becomes more anti-cyclonic on Sunday. Fewer clouds, less wind and more sunshine. Moisture from an approaching storm may allow some high level cloudiness to move in.
Sunday — • Mostly sunny, some high level cloudiness during the late afternoon. • High temperature 34.6º sd 0.7º (NBM model) Blue Bell. • Winds 10 mph gusts to 15
The wintry weather Monday evening into Tuesday looks to be a mixed precipitation event with snow mixing with sleet/freezing rain the back to snow. Final snow totals 1-2 inches by Tuesday morning, but expect changes in this forecast. Stay tuned.
For Sunday, the upper air low pressure system moves off to our east. The pressure gradient will cause it to be windy. An upper air wave approaches late in the day Still above average temperatures for January. (Seasonal average high is 40º and low is 23º Blue Bell.)
Sunday —
• Sunny in the morning, clouds move in towards noon. • High temperature 44.0 sd 1.1º (NBM model) Blue Bell. • Windy late morning and early afternoon WSW 12-15 mph with gusts to 20- 25 mph
Sat 08:46 AM Update — All models last night showed a several hour “dry slot” of clear skies this morning about 10 AM. (In past weeks, the recently updated HRRR v 4 has been particularly good at cloud cover forecasts)—
HRRR forecast for 10 AM today from last night’s model run (00z) (Click on image for a larger view.)
This morning’s 12z (7 AM) HRRR (High Resolution Rapid Refresh) model has reduced this area of clearing to a narrow area moving through about 10 AM—
HRRR model from 7 AM this morning (12z) showing narrow area of clearing. (Click on image for a larger view.)
I guess we’ll see if we get the brief clearing predicted. Cloud cover is one of the toughest weather parameters to get right.
Fri 9:10 PM- Updated Saturday and Sunday forecast below What had been thought would be a persistent pattern change starting this weekend is turning out to be a just a temporary dip in the jet flow this weekend; a return to non-eventful weather is expected for much of next week.
Regarding the dip in the jet flow this weekend, it’s best captured by the 1000-500mb “540 thickness line” (RED), which demarcates a colder, dense air mass from a milder air mass (often a dividing line for rain-snow)—
Canadian Global (GDPS) model surface forecast Saturday 7 AM showing 540 thickness line, upper atmosphere low pressure over Great Lakes and departing surface low pressure in the Northeast. (Click on image for a larger view.)
Saturday — • Showers end around daybreak. • A few hours of sun early, then considerable cloudiness much of the afternoon. • Widely scattered light sprinkles possible late afternoon or evening. Possible snow flurrymixes in. • High temperature 46.4 sd 1.5º early in the day, then slowly falling temps in the afternoon (NBM model) Blue Bell. • Breezy, winds WSW 9 mph with some gusts to 15 mph
For Sunday, the upper air low pressure system moves off to our east. The pressure gradient will cause it to be windy. An upper air wave approaches during the afternoon. Still above average temperatures for January. (Seasonal average high is 40º and low is 23º Blue Bell.)
Sunday — • Mostly sunny in the morning, cloudy in the afternoon. • High temperature 45.1º sd 1.0º (NBM model) Blue Bell. • WINDY, WSW 12-15 mph with gusts to 25 mph mid-day.
A mostly flat, zonal upper air flow for next week. Disturbances moving in this flow will bring cloudiness at times, despite the lack of any major storm development. In past winters, this might have been a setup for ice storms in the midwest at the air mass boundary, but a lack of extreme cold and a lack southern jet moisture seems to have ruled that out for the time being, but it’s something to watch out for—
Canadian Global for next Tuesday showing flat upper air flow. (Click on image for a larger view.)
I’ll update later this evening for any changes, but the forecast models have been fairly consistent over the past few days.
User Feedback Requested: Users, would you like to see all updates posted to Twitter or just the major new posts (as currently done)? Thanks!
Saturday Update: The period from January 16th through January 20th continues to show a strong signal for coastal low development and possible snow.
Low pressure that brought clouds on Friday will move east and away from us on Saturday. High pressure will build in on Saturday with mostly sunny skies, but occasional cloudiness from the upper air trough may move in late Saturday—
GFS Forecast 2 PM Saturday (Click on image for a larger view.)
Saturday—
Mostly sunny, some mid level cloudiness moves in during the mid afternoon.
High temperature 40.3º sd 1.4º (NBM model) Blue Bell.
Breezy, winds NNW 5-12 mph with some gusts to 20 mph mid-day.
The upper flow briefly becomes a slight ridge on Sunday. Skies on Sunday remain mostly sunny here as a low pressure system develops near the Gulp of Mexico—
GFS Forecast Sunday 2 PM
(Seasonal averages this week— high 40º low 24º Blue Bell)
Sunday—
• After early morning clouds, mostly sunny, • High temperature 41.9º sd 1.9º (NBM model) Blue Bell. • Light winds from the NW
The low pressure system developing on Saturday will pass to our south Monday into Tuesday. Most models (except the Canadian and German ICON) have the light snow shield missing us. The trend has been for the light snow/flurries shield to be a bit further north.
User Feedback Requested: Users, would you like to see all updates posted to Twitter or just the major new posts (as currently done)? Thanks!
Over the past several days, I’ve mentioned the new “parallel” GFS v 16 model and specifically wondered whether it was going to provide new insights into today’s weather forecast, specifically what sort of ‘precipitation type’ (the model parameter referred to as “PTYPE”— rain, sleet, freezing rain or snow) we would get with today’s storm.
The GFS v16 was one of the few models that were predicting snow at the precipitation onset; most of the higher resolution models (NAM, NAM-NEST, HIREF and HIRESW) were predicting freezing rain or rain. Indeed, I thought there might be a ‘cold bias’ with the new GFS that would need to be discounted. But not so. The GFS v16 also has correctly predicted the snow and the changeover to rain that is occurring as I write this. (The GFS PTYPE forecast from Saturday afternoon was posted in yesterday’s update.)
Let’s look at some other model forecasts from last night:
Here’s last night’s RAP (Rapid Refresh model)—
Sat evening’s RAP model (00z) showing snow and a mix.
And here’s last night’s HRRR—
Last night’s HRRR 00z (high Resolution Rapid Refresh) showing mostly rain.(Click on image for a larger view.)
In retrospect, last night’s model blend (NBM) correctly captured the snow onset instead of rain—
Saturday evening’s NBM (model blend) 00z for today, showing mostly snow or a mix. at the start.
So, if we ever get any real snow this season, we have the new GFS, RAP and NBM to rely on.
While we’re on the subject, the latest GFS 16 has the following snow totals by 1 AM Monday—
GFS v16 snow depth forecast for 1 AM Monday morning (Click on image for a larger view.)
As mentioned in another post, the temperatures north of us are running way too warm. The Climate models show above average temperatures to our north for the next month or two. So we might not be talking about all that much snow this season. Then again, warmer than average temperatures don’t necessarily translate into less snow or fewer storms. I guess we’ll see.
User Feedback Requested: Users, would you like to see all updates posted to Twitter or just the major new posts (as currently done)? Thanks!
