NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260405_1800
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 04/05 18Z 0.59 2521  95  43   2 0.00
Sun 04/05 19Z 0.75 2622  95  10   1 0.01
Sun 04/05 20Z 1.00 2623  96  17   0 0.01
Sun 04/05 21Z 1.50 2725  97  17  -1 0.02
Sun 04/05 22Z 2.00 2726  93  19  -2 0.02
Sun 04/05 23Z 1.99 2729  82  17  -3 0.00
Mon 04/06 00Z 1.36 2730  80  15  -3 0.00
Mon 04/06 01Z 1.66 2728  84  14  -4 0.00
Mon 04/06 02Z 1.37 2727  86  21  -4 0.00
Mon 04/06 03Z 1.55 2729  91  30  -5 0.00
Mon 04/06 04Z 1.71 2728  94  40  -6 0.00
Mon 04/06 05Z 1.81 2729  95  46  -7 0.00
Mon 04/06 06Z 1.82 2729  95  52  -7 0.00
Mon 04/06 07Z 1.69 2730  93  68  -8 0.00
Mon 04/06 08Z 1.11 2830  94  64  -8 0.00
Mon 04/06 09Z 1.08 2830  95  61  -8 0.00
Mon 04/06 10Z 1.18 2930  94  57  -8 0.00
Mon 04/06 11Z 1.42 2929  95  55  -9 0.00
Mon 04/06 12Z 2.16 2927  96  58 -10 0.00
Mon 04/06 13Z 2.36 2825  95  62 -10 0.00
Mon 04/06 14Z 3.18 2824  92  65 -10 0.00
Mon 04/06 15Z 3.79 2823  87  63 -10 0.00
Mon 04/06 18Z 12.10 2819  66  69  -8 0.00
Mon 04/06 19Z 12.01 2818  63  74  -8 0.00
Mon 04/06 20Z 11.22 2817  60  76  -7 0.00
Mon 04/06 21Z 11.19 2817  60  77  -7 0.00
Mon 04/06 22Z 10.65 2818  62  80  -7 0.00
Mon 04/06 23Z 7.56 2819  63  80  -8 0.00
Tue 04/07 00Z 3.06 2920  65  78  -8 0.00
Tue 04/07 01Z 1.38 3019  69  77  -8 0.00
Tue 04/07 02Z 0.99 3017  74  75  -9 0.00
Tue 04/07 03Z 0.88 3116  81  78 -10 0.00
Tue 04/07 04Z 0.72 3115  88  82 -10 0.00
Tue 04/07 05Z 0.43 3214  89  82 -10 0.00
Tue 04/07 06Z 0.41 3113  86  80 -11 0.00
Tue 04/07 07Z 0.43 3113  84  76 -11 0.01
Tue 04/07 08Z 0.47 3014  81  60 -11 0.00
Tue 04/07 09Z 0.46 3013  82  60 -11 0.00
Tue 04/07 10Z 0.47 2912  84  65 -12 0.00
Tue 04/07 11Z 0.50 2912  87  74 -12 0.00
Tue 04/07 12Z 0.50 2912  91  71 -12 0.00
Tue 04/07 13Z 0.52 2911  91  61 -12 0.00
Tue 04/07 14Z 0.79 2911  89  65 -12 0.00
Tue 04/07 15Z 1.51 3010  84  78 -12 0.00
Tue 04/07 16Z 2.33 3111  79  79 -12 0.00
Tue 04/07 17Z 4.16 3013  69  61 -13 0.00
Tue 04/07 18Z 4.65 3114  70  28 -13 0.00
Tue 04/07 19Z 4.73 3114  67  13 -13 0.00
Tue 04/07 20Z 4.45 3114  60   9 -13 0.00
Tue 04/07 21Z 3.93 3113  56  14 -13 0.00
Tue 04/07 22Z 2.76 3113  54  23 -13 0.00
Tue 04/07 23Z 0.78 3114  51  30 -13 0.00
Wed 04/08 00Z 0.68 3116  46  26 -13 0.00
Wed 04/08 01Z 0.89 3017  42  23 -13 0.00
Wed 04/08 02Z 0.96 3018  44  26 -14 0.00
Wed 04/08 03Z 0.82 3018  46  33 -14 0.00
Wed 04/08 04Z 0.64 3018  45  33 -14 0.00
Wed 04/08 05Z 0.57 3017  49  29 -14 0.00

Run total areal avg QPF for the Central_Greens is: 0.07 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