Figure 3-4. WST Example

METEOROLOGY FLIGHT PLANNING

CHAPTER THREE

WSUS41 KMKC 221855Z

WSTC

MKCC WST 221855

CONVECTIVE SIGMET 20C

VALID UNTIL 2055Z

ND SD

FROM 90W MOT-GFK-ABR-90W MOT

INTSFYG AREA SEV TS MOV FROM 24045KT. TS TOPS ABV FL450.

WIND GUSTS TO 60 KT RPRTD. +FC...HAIL TO 2 IN...WIND GUSTS

TO 65 KT POSS ND PTN.

CONVECTIVE SIGMET 21C

VALID UNTIL 2055Z

50SE CDS

ISOLD SEV TS D30 MOV FROM 24020KT. TS TOP ABV FL450.

HAIL 2 IN...WIND GUSTS TO 65 KT POSS.

OUTLOOK VALID 222055-230055

AREA 1...FROM INL-MSP-ABR-MOT-INL

SEV TS CONT TO DVLP IN AREA OVR ND. AREA IS EXP TO RMN SEV AND SPRD

INTO MN AS STG PVA MOV OVR VERY UNSTBL AMS WTH -12 LI.

AREA 2...FROM CDS-DEW-LRD-ELP-CDS

ISOLD STG SEV TS WILL DVLP OVR SWRN TX AND WRN TX THRU FCST PD AS

UPR LVL TROF MOV NEWD OVR VERY UNSTBL AMS. LI RMNS IN -8 TO -10

RANGE. DRY LN WILL BE THE FOCUS OF TS DVLPMT.

Figure 3-4 WST Example

For WSTs, a line of thunderstorms is defined as being at least 60 miles long with thunderstorms

affecting at least 40 percent of its length. Embedded thunderstorms, for the purpose of WSTs, are

defined as occurring within and obscured by haze, stratiform clouds, or precipitation from stratiform

clouds. WSTs for embedded thunderstorms are intended to alert pilots that avoidance by visual or

radar detection of the thunderstorm could be difficult or impossible. Note that the presence of

thunderstorms implies the associated occurrence of severe or greater turbulence, severe icing, and

low-level wind shear.

All issued and valid WSTs for a specified geographic area are collected and listed in one place: a

Convective SIGMET Bulletin. The three Convective SIGMET bulletin areas are the Eastern (E),

Central (C), and Western (W) US, separated by the 87 and 107 W lines of longitude (with

sufficient overlap to cover most cases when a phenomenon crosses the boundaries). These area

letters can be found in the heading portion of the message, after the message type (e.g., WSTC),

and after the WST bulletin number (e.g., 20C). Each of these three bulletins is transmitted hourly

(at +55 minutes) and is valid for up to 2 hours. If there are no conditions within a region meeting

Convective SIGMET criteria at the time of issuance, then a negative bulletin is sent.

SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS

3-11