Author: Weatherman

500 mB Height and Vorticity for Tuesday 27 June 2017 Source: wxmaps.org, GrADS/COLA After several days of generally lower pressure over most of the sub-continent, the South Atlantic high pressure cell made landfall during Wednesday. This saw a minor drop in night temperatures across Namibia south of Grootfontein. A bigger drop and much colder nights were experienced in the Karasburg and Keetmanshoop districts with the cold coming from the east. The week’s local weather was marked by several intrusions of moisture in the middle layers of the atmosphere roughly between 13,000 and 18,000 feet. Surface level humidity mirrored this...

Southern Hemisphere barometric pressure for Monday 19 June 2017 Source: wxmaps.org, GrADS/COLA   The selected map for this week’s weather discussion is the pressure forecast for next Monday, 19 June, showing a marked difference between expected conditions for next week, and this week’s weather. During this week, two single cold fronts and one linked front crossed south of Cape Agulhas. However, as was expected, the impact on Namibian weather was minimal. Over the largest part of southern Africa, high pressure conditions reigned with a weak anti-cyclonic circulation on the surface, and a more pronounced zonal, west to east, airflow...

Precipitation Forecast for Wednesday 14 June to Thursday 22 June Source: wxmaps.org, GrADS/COLA The weather map has been selected from the running series of one-week and two-week forecasts prepared daily by George Mason University in the USA. These maps are usually the most reliable longer-dated forecasts given the sophistication of the modelling on which they are based. But a forecast offers a view of the future and in meteorology, the future changes every second. The map above was published this Tuesday 04 June, based on current conditions then. By Friday it has become obsolete as can be seen from...

Precipitation Forecast for Wednesday 07 June 2017 Source: wxmaps.org, GrADS/COLA The relevant map for the weather discussion is the rainfall forecast for next Wednesday. It shows a strong low pressure system area ahead of an approaching frontal system with an extension into Namibia’s Sperrgebiet. These surface conditions are mirrored by mid-level developments indicating that the coming frontal system will have a considerably vertical depth, possibly extending as high as 25,000 feet up. This is not typical for the Western Cape winter. The synoptic development during this week corrobarates the expectation for improved rainfall over South Africa’s winter rainfall area,...

500 mB (18,000 feet) vorticity for Saturday 27 May 2017 Source: wxmaps.org, GrADS/COLA During this week the synoptic map has moved to a conventional winter pattern. The South Atlantic high pressure cell and the southern Indian high are spaced roughly equidistant west and east of the sub-continent with the South Atlantic high somewhat stronger at a respectable 1032 mB. The southern Indian high only managed to registed 1024 mB. The cores of both straddle the 33°S latitude indicating a stable winter position. In the absence of a strong low pressure system between the two highs, the cold front that...

Mean surface temperature from Friday 19 May to Saturday 27 May 2017 Source: wxmaps.org, GrADS/COLA This week the weather followed a regular intra-seasonal pattern with a marked shift to an early winter stance. The only exception is the continuing easterly to north-easterly wind flow on the surface, leading to pleasantly warm afternoons despite the early evening chill when the sun goes below the horison. When the larger synoptic pattern shifts from a summer to a winter stance, local Namibian weather displays the typical see-saw pattern where the days are summer days but the nights are almost winter nights. For...

Temperature forecast from Friday 05 May to Saturday 13 May 2017 Precipitation forecast from Friday 12 May to Friday 19 May 2017 Source: wxmaps.org, GrADS/COLA The two maps selected for this week’s discussion of local weather, cover two back to back weather windows. The first map shows the maximum temperatures for the one-week period starting this Friday 05 May indicating that for most of this period, Oosweer in some form, will impact the coastal weather. The second map is the expected rainfall, not for next week, but for the week after that from 12 to 19 May. It has...