STORMY MONDAY FOR SOUTHERN CALIFORNIA

Scattered rain showers will overspread the area by midday tomorrow. Periods of rain will persist into Monday night and then will taper early Tuesday morning. Most of San Diego County will see a half inch or less. Monday will also be a blustery day with winds gusting up to 35 mph. Mountain winds will gust as high as 60 mph.

Snow levels will start off at 4500-5500 feet early Monday and then drop to 3500-4500 feet by Monday night. This storm system is moving fast and doesn't have much moisture, so I'm expecting 2 to 4" above 3500 feet and 3 to 6" above 4500 feet. Isolated areas could get more. Definitely good news for Bear Mountain! In addition, parts of the central Sierra will easily see over a foot of new snow.

I've posted the snow outlook from two computer forecasts. The first one is from the RPM, which I think is accurate, while the second one (NAM) is too dry.

CALIFORNIA WEATHER OUTLOOK FOR THE REST OF FEBRUARY 2012

The weather should remain warm through Saturday, then we will see some cool changes next week. Unfortunately, I don't see much rain with this current pattern. I've posted two maps below which show temperature anomalies and precipitation anomalies over the past 30 days. It has been very dry and warm for most of the state.

The weather pattern will be dominated by northwest flow in the jet stream for the next several days. This means we will see a prolonged period of slightly cooler than average weather with an occasional warm day. I'm leaving the forecast dry through the end of February. We might eventually see a storm system sneak into our area by the first week of March.

VERIFICATION

ECMWF did an excellent job with the track of this storm. It showed hints of this storm eight days before it happened! I based my forecast on this model and did not waiver when the other models flip-flopped.

Within 48 hours, NAM generally did a good job with snow accumulations, though it was too ambitious with snow-to-liquid ratios (as expected). In addition, it was too far north in the early runs (as expected). RPM also did well within 36 hours. GFS was the worst.

I have to admit, there was definitely some luck mixed in with skill while making this forecast. I'm glad it panned out!

Here are the snow totals:

LAST UPDATE MID-ATLANTIC SNOW - SUNDAY MORNING

RPM always does very well during the day of a storm, and to be honest, I like this solution the best. I've gone for 3 to 6" in the Richmond metro all along, so there is no reason to change it now. Be sure to check with your local meteorologist for the latest with this storm.

As expected, the NAM shifted back north. I still think it's too far south though. All in all a somewhat plausible solution.

GFS...well...we'll see if this happens...doubt it.

UPDATE ON MID-ATLANTIC SNOW - SATURDAY NIGHT

The latest data is significantly different than earlier today. The NAM still shows the most plausible precip field. It shows the persistent band of snow reaching all the way to the coast. However, it has shifted the snow band about 50 miles south. Although I anticipated a southerly trend, this is again too much. 

I would shift this map up about 20 miles. I would also take a couple inches off the totals in Central Virginia. I'm not expecting a 10:1 snow-to-rain ratio for the entire event (warm ground and surface temps and the possibility of some sleet).

I want to also mention that I think it's odd how the NAM/GFS MOS data keep dew points near 30 all day tomorrow, yet when it starts raining, they keep surface temps in the lower 40s. That's nonsense! Temps will rapidly fall at the onset of precipitation from evaporative cooling. Dew points tonight are in the mid 20s, so the models are already wrong...just food for thought.

I might as well stick with my 3 to 6" forecast in the Richmond metro area. Isolated areas will pick up more.

RPM also shifted south.

GFS is either going to be hailed as the best model ever or it's going to be considered the ultimate bust machine. This model stands alone with its' forecast in Central Virginia...1" or less. Wow! I still can't think of a reason why the snow band would completely dissipate as the storm system strengthens. It just doesn't make sense. If the GFS is right, I will gladly eat crow on Monday. Again, I would rather get people prepared for this storm than downplay it.

WEATHER UPDATE ON MID-ATLANTIC SNOW - SATURDAY AFTERNOON

After looking at the latest data, I still like the NAM solution to this event. It generally matches what the ECMWF has been showing all along. With that said, the maps below represent a 10:1 snow-to-liquid ratio. Parts of this event will have a lower ratio due to wet snow, warm ground temperatures and the possibility of some sleet. I would take off a couple inches from the NAM totals for Central and Eastern Virginia.

I'm keeping with my 3 to 6" forecast for Richmond. Isolated areas in Central Virginia will get more.

RPM also shows a plausible solution, though I'm sad that the 12Z data is unavailable. The 15Z data shows an explosion of 6 to 8" of snow in Central Virginia. This is probably caused by the rapid strengthening of the storm as it moves off the coast. Precipitation rates will increase and bring colder air down from aloft. 

The GFS continues to change its' solution each run. The key here is the strength of the storm. GFS never has the central pressure dropping below 1000 MB unlike the NAM and ECMWF, which have the pressure dropping to 996 MB. A weaker storm means weaker cold air advection - both horizontally and vertically.

I'm not buying this solution. This storm "over-achieved" what the models predicted here along the West Coast, so the same could occur farther east. I think it's better to be prepared for a snow event than to be surprised Monday morning with 6" of snow on the ground. Worst case scenario...GFS is right and I'm eating crow Monday morning.

WEATHER UPDATE ON MID-ATLANTIC SNOW - FRIDAY NIGHT

Here are some brief thoughts on the latest data:

• GFS is out to lunch. How can the band of snow magically disappear once it moves into the eastern half of VA? However, if it continues to show the same scenario for tomorrow's 12Z and 00Z runs, I might be a little worried.
• What happened to the NAM? I expected a slight shift south, but this is ridiculous. I expect a dramatic shift back northward tomorrow morning.
• ECMWF has shifted *slightly* northward. Wobbling is to be expected as the storm approaches. ECMWF ensemble never ceases to amaze me when it comes to these type of storms. It's the best medium to long range forecasting tool.
• RPM snow accumulations match the ECMWF storm track. It has the best solution this evening.

Right now I'm keeping with my 3 to 6" forecast for Richmond. Here are factors that can ruin my forecast: 

1. Surface temperatures
2. Ground temperatures
3. Prolonged period of sleet
4. Shift in the track of the storm

The data tomorrow will be more reliable, so don't get too excited (or sad) until then.

WEATHER UPDATE ON MID-ATLANTIC SNOW - FRIDAY AFTERNOON

The only change from last night's data is a slight shift south, which has been the progressive trend over the past few days. It's definitely something to watch over the next 24 hours.

This storm was a beast along the West Coast. It dumped significant snow in the mountains of Southern California. There is no reason to believe it won't do the same for parts of Tennessee, Kentucky, West Virginia, Virginia and Maryland.

I don't have time to draw a detailed map, but I'm liking the 12Z NAM solution with this storm. I might shift the accumulations south by about 10 miles. That would put Richmond in the 3 to 6" range.

Remember, this is just an educated guess. I would encourage you to follow meteorologist in your region for more detailed information on this potentially dangerous storm. I'll try and have another update tonight when I get home.

MID-ATLANTIC SNOW - THURSDAY NIGHT UPDATE

There are little changes in the latest data. The storm has slowed down and shifted slightly south. I decided to post the last five runs of the ECMWF ensemble mean (1000-500 MB thickness and MSLP). You will notice the trend of a slower and stronger storm. However, the model has not trended cooler. If fact, you can see in the latest run (posted below), the ensemble mean keeps temps in the mid to lower 30s in Central Virginia Sunday evening.

This is a potent storm and it can "make" its' own cool air by pulling it down from aloft via heavy precipitation. However, these marginal temps will eat away from the totals. It is also important to watch mid-level temperatures (5,000 to 10,000 feet) because a warm layer could produce sleet for a couple hours. This could also eat away from the accumulations. Nonetheless, this is a massive storm and it will produce some impressive snow totals.

I'm still sticking with my snow map posted earlier today. I hope to have another update tomorrow.

MID-ATLANTIC SNOW THURSDAY UPDATE

The ECMWF ensemble mean has nailed this storm from the very beginning - it showed hints of this storm last Saturday! There is no need to look at any other computer model at this point. Not until 36 to 48 hours before the storm hits. Surface temperatures in Central Virginia will be a concern early Sunday, but this storm will bring down cold air aloft, so accumulations should begin late in the day.

Right now the only unknown is the exact track of this storm. This will allow us to pinpoint the location of the heaviest band of snow. 

Click on the images below to enlarge:

SAN DIEGO COUNTY RAIN TOTALS FROM WEDNESDAY 2/15/2012

UPDATE ON MID-ATLANTIC SNOW

No major changes in the 00Z data (unless you are following the worthless GFS). It sill looks like there will be a major low pressure forming with a narrow band of heavy wet snow. Now we get to decide where! I would wait at least one more day before things start becoming more concrete.

STORM EXPECTED TO GO COAST-TO-COAST

Scattered rain showers will overspread Southern California this afternoon and evening. Rain totals will be about a quarter inch along the coast and inland, though totals could climb to an inch in the mountains. The atmosphere will be somewhat unstable, so an isolated thunderstorm could pop up in the evening. This could bring a brief downpour and higher rain totals.

Snow levels will drop to 4000-5000 feet. Elevations above this could pick up 2 to 4" of fresh snow with the higher elevations receiving 4 to 12". Most of this will occur in the San Bernardino Mountains, which you can see on the map below.

This same storm system will dive into the Northern Baja, move across Texas and then race up towards the Mid-Atlantic. This storm will be lacking cold air, so it will produce a lot of rain for the upcoming weekend. The first map below shows the low developing and the second map shows surface temperatures. 

The system will rapidly intensify once it moves off the coast Sunday evening. Surface temperatures will still be very warm (according to this model), however, heavier precip could bring down some colder air aloft. Regardless, 35 degrees is typically the magic number in central Virginia for the rain/snow line. If it can get below 35, then there could be a brief period of heavy wet snow.

I'm guessing that this storm will produce a very narrow band of snow 3 to 6" (just a hunch). It's too early to speculate where this might fall...if at all.

RAIN TOTALS FROM MONDAY, 2/13/2012

San Diego & Southern California Outlook - February 12-29

Straight To The Point
Southern California will have several chances for rain during the second half of February. This could possibly bring our rain totals up to near normal for the entire month. However, I don't see any heavy-duty rain events on the horizon...just light to moderate stuff here and there.

Isolated showers are possible late tomorrow into early Tuesday. Another round of rain will arrive Wednesday and Wednesday night. A couple showers could pop up on Sunday, but the brunt of the storm will miss us to the east (don't cancel your outdoor plans). We will see a brief break in the action early next week, then the pattern returns for the end of the month.

Temperatures will remain near normal for the rest of this month - mid 60s along the coast, upper 60s inland. The only exception will be a brief warm period early next week.

Technical
Upper level flow will not support any major storms for the immediate future (the rest of this month). Instead, we will see a series of shortwaves diving out of the Gulf of Alaska and into our region. I've labelled them on the map below:

The pattern will briefly erode early next week as a ridge nudges this way. GFS is very aggressive with this warm up, though I tend to side with the more reliable ECMWF. Regardless, the first half of next week looks mainly dry and mild.

This pattern vaguely reminds me of last November, when I speculated that it might return for the end of this winter. Here is an excerpt from my winter outlook written in November:

I expect the pattern to briefly shift and then return later this winter. During that time, we could see the worst snow storms of the season across the Midwest and possibly farther east...depending on the storm track and availability of cold air.

I have to admit: this is not an original idea of mine. I have a colleague who swears up and down that late autumn patterns tend to cycle through the winter. There might actually be some truth in his thinking. In fact, most ensembles are hinting at this pattern persisting through the end of this month. Right now it looks like the storm track will favor heavy snows for the Southern/Mid Rockies and into the Upper Midwest. We'll see if it will shift farther east for the Mid-Atlantic and East Coast.