Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260302_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 03/02 00Z 0.41 3016  66  35 -17 0.00
Mon 03/02 01Z 0.42 3120  63  32 -18 0.00
Mon 03/02 02Z 0.37 3121  57  24 -18 0.00
Mon 03/02 03Z 0.30 3120  51  15 -18 0.00
Mon 03/02 04Z 0.25 3220  48  10 -19 0.00
Mon 03/02 05Z 0.22 3220  47   8 -19 0.00
Mon 03/02 06Z 0.19 3218  46   6 -19 0.00
Mon 03/02 07Z 0.19 3217  44   4 -19 0.00
Mon 03/02 08Z 0.18 3115  44   5 -19 0.00
Mon 03/02 09Z 0.19 3115  43   7 -19 0.00
Mon 03/02 10Z 0.21 3115  41  10 -19 0.00
Mon 03/02 11Z 0.23 3015  40  12 -19 0.00
Mon 03/02 12Z 0.25 3014  40  16 -19 0.00
Mon 03/02 13Z 0.27 2914  42  19 -19 0.00
Mon 03/02 14Z 0.27 2913  43  24 -19 0.00
Mon 03/02 15Z 0.29 2913  44  23 -18 0.00
Mon 03/02 16Z 0.30 2913  42  19 -18 0.00
Mon 03/02 17Z 0.31 2912  38  15 -17 0.00
Mon 03/02 18Z 0.32 2912  37  16 -17 0.00
Mon 03/02 19Z 0.33 2911  39  24 -16 0.00
Mon 03/02 20Z 0.33 2810  43  33 -16 0.00
Mon 03/02 21Z 0.32 2710  46  38 -15 0.00
Mon 03/02 22Z 0.31 2610  47  33 -14 0.00
Mon 03/02 23Z 0.33 2612  46  31 -13 0.00
Tue 03/03 00Z 0.31 2513  44  36 -12 0.00
Tue 03/03 01Z 0.34 2514  43  41 -11 0.00
Tue 03/03 02Z 0.35 2516  38  51 -10 0.00
Tue 03/03 03Z 0.41 2520  33  60  -9 0.00
Tue 03/03 04Z 0.45 2522  30  67  -8 0.00
Tue 03/03 05Z 0.47 2523  34  75  -8 0.00
Tue 03/03 06Z 0.47 2523  31  69  -7 0.00
Tue 03/03 07Z 0.46 2523  33  60  -6 0.00
Tue 03/03 08Z 0.43 2522  34  53  -5 0.00
Tue 03/03 09Z 0.41 2421  34  51  -5 0.00
Tue 03/03 10Z 0.40 2421  31  52  -4 0.00
Tue 03/03 11Z 0.39 2321  28  49  -4 0.00
Tue 03/03 12Z 0.38 2320  27  45  -3 0.00
Tue 03/03 13Z 0.38 2321  30  43  -3 0.00
Tue 03/03 14Z 0.39 2323  38  38  -2 0.00
Tue 03/03 15Z 0.38 2324  48  35  -2 0.00
Tue 03/03 16Z 0.41 2324  58  34  -2 0.00
Tue 03/03 17Z 0.43 2325  68  30  -2 0.01
Tue 03/03 18Z 0.45 2324  78  26  -2 0.01
Tue 03/03 19Z 0.48 2324  89  23  -3 0.01
Tue 03/03 20Z 0.50 2324  96  30  -3 0.01
Tue 03/03 21Z 0.48 2323  97  58  -3 0.02
Tue 03/03 22Z 0.47 2323  97  81  -3 0.03
Tue 03/03 23Z 0.41 2221  97  88  -2 0.03
Wed 03/04 00Z 0.43 2221  97  87  -2 0.03
Wed 03/04 01Z 0.47 2222  98  89  -3 0.03
Wed 03/04 02Z 0.51 2321  98  96  -3 0.04
Wed 03/04 03Z 0.51 2419  98  97  -3 0.03
Wed 03/04 04Z 0.45 2517  98  95  -3 0.02
Wed 03/04 05Z 0.43 2616  98  85  -3 0.02
Wed 03/04 06Z 0.32 2814  96  84  -2 0.01
Wed 03/04 07Z 0.20 3012  92  58  -1 0.00
Wed 03/04 08Z 0.13 3111  84  33   0 0.00
Wed 03/04 09Z 0.12 3111  72  24   0 0.00
Wed 03/04 10Z 0.16 3113  64  26   0 0.00
Wed 03/04 11Z 0.15 3113  60  21   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1