Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260610_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 06/10 06Z 0.30 2708  71   1  16 0.00
Wed 06/10 07Z 0.35 2708  74   4  15 0.00
Wed 06/10 08Z 0.35 2708  77  18  15 0.00
Wed 06/10 09Z 0.31 2607  77  37  15 0.00
Wed 06/10 10Z 0.24 2506  78  59  15 0.00
Wed 06/10 11Z 0.24 2307  79  76  15 0.00
Wed 06/10 12Z 0.25 2208  82  81  15 0.00
Wed 06/10 13Z 0.25 2209  85  80  15 0.00
Wed 06/10 14Z 0.24 2110  88  81  15 0.00
Wed 06/10 15Z 0.28 2110  89  87  15 0.00
Wed 06/10 16Z 0.26 2010  90  83  15 0.00
Wed 06/10 17Z 0.28 1910  90  86  16 0.00
Wed 06/10 18Z 0.48 2011  91  90  16 0.01
Wed 06/10 19Z 0.61 2113  90  93  16 0.02
Wed 06/10 20Z 0.40 2115  89  91  16 0.03
Wed 06/10 21Z 0.47 2116  88  86  16 0.02
Wed 06/10 22Z 0.43 2113  90  87  16 0.00
Wed 06/10 23Z 0.38 2113  92  88  16 0.03
Thu 06/11 00Z 0.32 2114  94  87  16 0.05
Thu 06/11 01Z 0.36 2116  96  90  16 0.07
Thu 06/11 02Z 0.36 2116  96  86  16 0.11
Thu 06/11 03Z 0.45 2318  97  90  16 0.07
Thu 06/11 04Z 0.41 2415  95  80  16 0.13
Thu 06/11 05Z 0.45 2416  94  83  16 0.05
Thu 06/11 06Z 0.51 2517  96  83  16 0.02
Thu 06/11 07Z 0.58 2618  96  81  16 0.03
Thu 06/11 08Z 0.55 2718  93  75  16 0.02
Thu 06/11 09Z 0.55 2718  94  69  16 0.01
Thu 06/11 10Z 0.60 2719  95  74  15 0.01
Thu 06/11 11Z 0.61 2819  96  68  15 0.01
Thu 06/11 12Z 0.53 2817  95  68  15 0.01
Thu 06/11 13Z 0.53 2816  96  69  15 0.01
Thu 06/11 14Z 0.43 2814  93  48  16 0.01
Thu 06/11 15Z 0.31 2910  88  30  17 0.00
Thu 06/11 16Z 0.32 2809  87  43  17 0.00
Thu 06/11 17Z 0.51 2711  89  51  17 0.00
Thu 06/11 18Z 0.55 2712  91  53  17 0.00
Thu 06/11 19Z 0.55 2613  95  64  17 0.02
Thu 06/11 20Z 0.57 2714  95  67  17 0.02
Thu 06/11 21Z 0.58 2615  96  71  17 0.01
Thu 06/11 22Z 0.59 2716  90  71  18 0.01
Thu 06/11 23Z 0.71 2817  92  73  17 0.02
Fri 06/12 00Z 0.66 2916  92  66  17 0.00
Fri 06/12 01Z 0.54 2815  93  65  16 0.04
Fri 06/12 02Z 0.44 2814  94  56  16 0.08
Fri 06/12 03Z 0.35 2812  90  50  16 0.01
Fri 06/12 04Z 0.34 2813  90  51  16 0.00
Fri 06/12 05Z 0.31 2912  92  61  16 0.00
Fri 06/12 06Z 0.33 2912  92  69  16 0.01
Fri 06/12 07Z 0.40 2914  94  69  16 0.01
Fri 06/12 08Z 0.47 2917  97  74  15 0.02
Fri 06/12 09Z 0.48 2918  97  74  15 0.04
Fri 06/12 10Z 0.42 2915  95  74  15 0.02
Fri 06/12 11Z 0.37 2913  91  74  15 0.01
Fri 06/12 12Z 0.31 2911  90  67  15 0.01
Fri 06/12 13Z 0.27 2809  87  54  16 0.00
Fri 06/12 14Z 0.14 2805  77  38  17 0.00
Fri 06/12 15Z 0.15 2705  71  26  18 0.00
Fri 06/12 16Z 0.29 2708  72  27  18 0.00
Fri 06/12 17Z 0.32 2809  66  32  18 0.00

Run total areal avg QPF for the greens is: 1.05 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