Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260301_1200
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)
=== ===== === ==== ==== === === === ====
Sun 03/01 12Z 0.19 3213  87  88 -12 0.00
Sun 03/01 13Z 0.17 3217  85  72 -13 0.00
Sun 03/01 14Z 0.20 3217  77  53 -13 0.00
Sun 03/01 15Z 0.29 3118  73  43 -13 0.00
Sun 03/01 16Z 0.32 3120  72  42 -14 0.00
Sun 03/01 17Z 0.34 3120  70  30 -15 0.00
Sun 03/01 19Z 0.50 3119  70  30 -16 0.00
Sun 03/01 20Z 0.51 3119  74  38 -17 0.00
Sun 03/01 21Z 0.53 3119  77  47 -17 0.00
Sun 03/01 22Z 0.54 3119  80  53 -17 0.00
Sun 03/01 23Z 0.53 3020  78  59 -18 0.00
Mon 03/02 00Z 0.54 3021  74  53 -19 0.00
Mon 03/02 01Z 0.47 3122  65  41 -19 0.00
Mon 03/02 02Z 0.37 3122  55  29 -19 0.00
Mon 03/02 03Z 0.31 3121  49  21 -19 0.00
Mon 03/02 04Z 0.28 3121  47  16 -19 0.00
Mon 03/02 05Z 0.27 3120  46  12 -19 0.00
Mon 03/02 06Z 0.26 3119  44   9 -19 0.00
Mon 03/02 07Z 0.26 3119  42   7 -19 0.00
Mon 03/02 08Z 0.27 3119  40   6 -19 0.00
Mon 03/02 09Z 0.28 3119  41   7 -19 0.00
Mon 03/02 10Z 0.28 3018  42   8 -19 0.00
Mon 03/02 11Z 0.31 3019  47   9 -19 0.00
Mon 03/02 13Z 0.36 2920  55  18 -19 0.00
Mon 03/02 14Z 0.36 2919  55  18 -19 0.00
Mon 03/02 15Z 0.37 2918  52  19 -19 0.00
Mon 03/02 16Z 0.40 2917  46  19 -18 0.00
Mon 03/02 17Z 0.41 2917  40  17 -18 0.00
Mon 03/02 18Z 0.38 2916  39  14 -17 0.00
Mon 03/02 19Z 0.36 2914  41  14 -16 0.00
Mon 03/02 20Z 0.32 2912  41  12 -15 0.00
Mon 03/02 21Z 0.32 2812  41   9 -14 0.00
Mon 03/02 22Z 0.32 2712  42  15 -13 0.00
Mon 03/02 23Z 0.33 2613  42  33 -13 0.00
Tue 03/03 00Z 0.35 2515  43  50 -12 0.00
Tue 03/03 01Z 0.40 2418  39  50 -11 0.00
Tue 03/03 02Z 0.45 2422  33  62 -10 0.00
Tue 03/03 03Z 0.51 2425  26  58  -9 0.00
Tue 03/03 04Z 0.56 2528  29  57  -8 0.00
Tue 03/03 05Z 0.57 2529  29  55  -7 0.00
Tue 03/03 06Z 0.57 2530  27  55  -6 0.00
Tue 03/03 07Z 0.55 2529  29  55  -5 0.00
Tue 03/03 08Z 0.53 2527  29  53  -4 0.00
Tue 03/03 09Z 0.50 2526  30  50  -4 0.00
Tue 03/03 10Z 0.50 2526  30  46  -4 0.00
Tue 03/03 11Z 0.50 2426  30  42  -3 0.00
Tue 03/03 12Z 0.48 2425  29  37  -3 0.00
Tue 03/03 13Z 0.45 2424  34  29  -3 0.00
Tue 03/03 14Z 0.43 2424  40  23  -2 0.00
Tue 03/03 15Z 0.44 2325  49  16  -2 0.00
Tue 03/03 16Z 0.46 2326  61  14  -2 0.00
Tue 03/03 17Z 0.48 2326  77  12  -2 0.00
Tue 03/03 18Z 0.51 2327  88  13  -3 0.00
Tue 03/03 19Z 0.52 2326  93  17  -3 0.00
Tue 03/03 20Z 0.51 2326  95  34  -3 0.01
Tue 03/03 21Z 0.46 2324  96  38  -2 0.01
Tue 03/03 22Z 0.40 2321  96  61  -1 0.01
Tue 03/03 23Z 0.36 2320  96  91   0 0.01

Run total areal avg QPF for the Central_Greens is: 0.04 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