Tag: Rain

Wet & Windy Weather On The Way

Brad Leave a comment

Yesterday’s beautiful mid-October weather will be replaced in a hurry today and tomorrow, as a intense 985mb low pressure system brings unsettled weather into the Red River Valley with strong winds moving across the area as the low pushes eastwards.

RDPS 3hr. QPF for this afternoon.

3-hour accumulated precipitation for mid-afternoon from the RDPS. Precipitation will be oriented in a band NW-SE ahead of the main surface trough.

Cloudy skies will be dominant over the Red River Valley over the next couple days. While temperatures are fairly mild this morning, and of note is how high our dewpoint has climbed, we won’t gain too much temperature-wise through the day today. Showers will push into portions of the Red River Vally & SE Manitoba this morning, however it’s likely that precipitation will be sporadic for any one location through the day today with fairly minimal accumulations. Conditions don’t look too favourable for drizzle today; you generally want saturated low-levels of the atmosphere with a sharp contrast into dry air immediately above the cloud deck for drizzle generation. Today, we’ll actually have dryer low-levels with a fairly moist atmosphere above, so it’s more likely that any light precipitation would be somewhat-evaporated rain, not drizzle. Temperatures will climb to 12 or 13°C today.

A band of steady rain will begin to push into the Red River Valley this evening as an area of strong frontogenesis1 on the northwest side of the 850mb low orients itself over the region. The band of rain looks to be fairly narrow, and positioning of it will be very sensitive to the positioning of the 850mb low. All areas in the Red River Valley will see some periods of rain tonight, however any locations that end up under this sharp band of rain will likely see 5-10mm of rain. Amounts remain low, despite the strong forcing, as this system, while energetic, is relatively low in moisture. Precipitable water values look to be only in the 20-25mm range, instead of the closer to 40-50mm range we look for for higher-accumulation rainfall events.

Winds will pick up overnight into Thursday as the Red River Valley moves into a strong pressure gradient on Thursday. Winds will climb to 40-50km/h with gusts up to 60km/h. Showers will be widespread through the Valley as general “wraparound” precipitation moves in on the backside of this system. Total amounts for tomorrow will generally be 4-8mm across the Red River Valley. The rain and wind will taper off tomorrow night as the system moves off towards the Great Lakes. Temperatures will drop down to 6 or 7°C.

Friday will be a slow recovery day, as the clouds will begin to break up a bit through the day. With skies remaining fairly cloudy with only a few breaks for sunshine, temperatures will end up fairly steady through the day; likely only around 8°C. Looking ahead to the weekend, it looks to be a fairly seasonal weekend with a mix of sun and clouds and highs near the seasonal 10°C.

  1. From the AMS Glossary: In general, an increase in the horizontal gradient of an airmass property, principally density, and the development of the accompanying features of the wind field that typify a front. ↩

Gloomy Thanksgiving Monday

Brad Leave a comment

This Thanksgiving will be nothing like last year’s (which featured temperatures in the twenties), as rain and wet snow make for a rather miserable holiday Monday.

Total precipitation accumulation for Monday's system

The GEM model shows generally 10-20mm of precipitation over Southern Manitoba

A low pressure system sliding south-eastward through Manitoba on Monday will be responsible for the precipitation, with rain beginning to move into Southern Manitoba early Monday morning. Temperatures on Monday will be cool, but generally not cold enough for snow with values hovering in the mid single digits during the daytime. By evening there will be a changeover to snow in some areas, mainly portions of Western Manitoba, as colder air is pulled down from the north. Areas in the Red River Valley can expect a bit of wet snow late Monday evening into the overnight period, but with surface temperatures remaining above zero, no notable accumulation is expected. Total precipitation accumulations will generally range from 10 to 20mm across Southern Manitoba by early Tuesday.

Unfortunately, conditions will improve little for Tuesday. It will be a chilly start to the work-week as cold air pulled down by the previous day’s low pressure system will not allow temperatures to climb much higher than the mid single digits at best. Monday’s low pressure system will have departed by Tuesday morning, so no more significant precipitation is expected (save for perhaps a few scattered showers or flurries). At this point models keep us in the single digits for Wednesday as well, so even normal weather will continue to elude us.

The late week period looks to remain fairly miserable, with temperatures staying stuck in the single digits. No more significant precipitation is expected later this week.

Elsewhere in Weather News: September 1st, 2012

Matthieu Leave a comment

Tropical Depression Isaac: Update

What was once dubbed Hurricane Isaac when it made landfall as a category one hurricane, is now considered a ‘tropical depression’. Isaac continues to pose a threat a week after it made landfall but it has weakened significantly, and will continue to do so, as it penetrates further into the southern half of Continental United States. Although this hurricane was “only” rated a category one when it made landfall, comprising of maximum sustained winds of 135km/h at peak intensity, you would have not guessed the incredible amounts of rain it brought into Louisiana and surrounding Gulf States. Here are a couple of the most impressive rainfall totals recorded throughout the whole event:

-In Gretna, LA, the National Hurricane Center (NHC) unofficially reported 466mm of rainfall.
-In New Orleans, LA, 510mm of rainfall was reported, breaking New Orleans’ old daily rainfall record by 48mm (a record thsat was set by Hurricane Katrina).
-In Kiln, MS (west of Gulfport) 433mm of rainfall was reported.

Not only did Hurricane Isaac bring with it enormous amounts of rain, the storm surge that accompanied it was quite severe. Wind-driven storm surge is mostly caused by the severe winds accompanying a hurricane. These winds push ocean waters towards land similar to a wave but larger in size (in this case with south winds) and in turn, ocean levels are higher than the normal tide. This phenomena makes for serious flooding along the Gulf Coast since the terrain along the Gulf of Mexico is not mountainuous – it is more of a gradual slope. When ocean water then rises, it is easy for it to move inland quickly.

Isaac storm surge

Hurricane Isaac’s wind direction depicted with arrows. Blue boxes along the shoreline show areas where winds were favorable for storm surge. Green arrows (north winds) is where storm surge was less favorable because of the wind direction. Picture was taken just before landfall on the night of August 28th. (Source: NOAA)

In Louisiana, two people lost their lives in the Plaquemines Parish, one of the hardest hit parishes, as the tide rolled in and consumed their house. This now brings the Hurricane Isaac death toll in the United States to four, with damages listed in the hundreds of millions. In Louisiana and Mississippi, power was out to over a million people and it was estimated that 75% of New Orleans was out of power when the eye wall passed closest to the city. For a storm being of weak category one, it did an extensive amount of damage. This was in part caused by it’s broad area of precipitation, large area extending out from the eye of tropical storm force winds, extremely slow movement, and storm surge levels you would expect form a category two or three hurricane.

Flooding

Residents evacuating in Lafitte, LA by boat because of flooding. (Source: Yahoo News)

This week in the tropics there are three other notable storms: Hurricane Kirk out in the middle of the Atlantic which poses no threat to land; Tropical Storm Leslie which does not pose a threat to the United States but as it strengthens, could pose a threat to Bremuda; and lastly, Hurricane Ileana out in the Eastern Pacific poses no threat to land but could cause high surf to the Baja Peninsula.

Stormy Night Ahead; Cooler Weekend

Brad Leave a comment

Another 30°C+ day will give way to stormier weather tonight as a cold front pushes across Southern Manitoba. We’ll see a slightly cooler weekend than the weather of late as we remain in the cooler air behind this system.

Precipitable Water for Friday Night

Precipitable water from the GEM-REG as the cold front pushes into the RRV tonight. Elevated values of 40-50mm through the RRV indicate the potential for stronger storms with locally heavy rainfall.

We’ll see temperatures climb into the low 30’s across Southern Manitoba again today as we remain under the influence of a pool of warm air entrenched over the Eastern Prairies. After some of this morning’s debris cloud from last night’s nocturnal convection clears out, here in Winnipeg we’ll climb to a high near 31 or 32°C, while areas to our south could reach as high as 33°C today.

Things will change promptly this evening as a cold front pushes across the province. Showers and thunderstorms will develop along the front in the early to mid-evening and continue to grow in coverage as the night progresses. This line of showers and thunderstorms will move through the Red River Valley overnight, bringing 5-15mm of rain to the region, the potential for some areas to see a bit over 1” total accumulation, and hopefully a good light show. These storms are not expected to be severe, and could potentially be one of the last night-time light shows we’ll get in 2012.

Tomorrow we’ll see a daytime high only around 24°C with a southwesterly wind at 20-30km/h. Sunday will reach about 25°C with lighter winds. Skies should be mostly sunny both days, with just an occasional cloudy patch here and there.

Temperatures are expected to climb back towards the 30°C mark through the first half of next week.