NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260829_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)
=== ===== === ==== ==== === === === ====
Sat 08/29 12Z 0.08 3413  65   5   6 0.00
Sat 08/29 13Z 0.12 3310  65   7   7 0.00
Sat 08/29 14Z 0.21 3209  68   7   7 0.00
Sat 08/29 15Z 0.43 3107  70   7   7 0.00
Sat 08/29 16Z 0.95 3007  70   7   7 0.00
Sat 08/29 17Z 1.43 2905  69   6   8 0.00
Sat 08/29 18Z 1.71 2706  69   7   8 0.00
Sat 08/29 19Z 1.79 2507  72   6   8 0.00
Sat 08/29 20Z 2.16 2509  80   5   8 0.00
Sat 08/29 21Z 0.94 2410  79   5   9 0.00
Sat 08/29 22Z 0.57 2412  75   6   9 0.00
Sat 08/29 23Z 0.57 2414  76   7  10 0.00
Sun 08/30 00Z 0.72 2518  74   9  10 0.00
Sun 08/30 01Z 0.87 2521  72   9  10 0.00
Sun 08/30 02Z 0.84 2622  69  16  11 0.00
Sun 08/30 03Z 0.86 2724  68  28  11 0.00
Sun 08/30 04Z 0.90 2725  68  39  11 0.00
Sun 08/30 05Z 0.98 2727  70  48  11 0.00
Sun 08/30 06Z 1.12 2730  73  55  11 0.00
Sun 08/30 07Z 1.21 2730  71  53  11 0.00
Sun 08/30 08Z 1.11 2728  69  44  12 0.00
Sun 08/30 09Z 1.07 2727  70  52  12 0.00
Sun 08/30 10Z 0.99 2726  70  50  12 0.00
Sun 08/30 11Z 1.01 2726  70  48  11 0.00
Sun 08/30 12Z 0.95 2726  73  54  11 0.00
Sun 08/30 13Z 0.89 2724  72  42  12 0.00
Sun 08/30 14Z 0.88 2723  73  46  12 0.00
Sun 08/30 15Z 0.93 2621  74  45  12 0.00
Sun 08/30 16Z 0.96 2619  73  47  12 0.00
Sun 08/30 17Z 1.11 2519  74  52  12 0.00
Sun 08/30 18Z 1.27 2519  78  56  12 0.00
Sun 08/30 19Z 1.25 2520  83  79  12 0.01
Sun 08/30 20Z 1.03 2517  74  85  12 0.00
Sun 08/30 21Z 1.17 2518  86  92  12 0.01
Sun 08/30 22Z 1.15 2520  89  96  11 0.02
Sun 08/30 23Z 0.85 2620  82  95  11 0.03
Mon 08/31 00Z 0.86 2620  89  98  11 0.03
Mon 08/31 01Z 0.67 2719  94  98  11 0.06
Mon 08/31 02Z 0.58 2819  94  92  11 0.06
Mon 08/31 03Z 0.47 3019  96  84  10 0.02
Mon 08/31 04Z 0.31 3218  93  80  10 0.01
Mon 08/31 05Z 0.28 3116  91  74  10 0.01
Mon 08/31 06Z 0.18 3317  92  66  10 0.01
Mon 08/31 07Z 0.06 3416  87  33  11 0.01
Mon 08/31 08Z 0.05 3514  83   9  10 0.00
Mon 08/31 09Z 0.05 3513  75   4  11 0.00
Mon 08/31 10Z 0.03 3511  69   4  10 0.00
Mon 08/31 11Z 0.03 3511  63   5  10 0.00
Mon 08/31 12Z 0.02 3510  58   6  10 0.00
Mon 08/31 13Z 0.02 3509  54   7  11 0.00
Mon 08/31 14Z 0.01 3407  53   8  11 0.00
Mon 08/31 15Z 0.02 3406  54  10  11 0.00
Mon 08/31 16Z 0.03 3304  56  13  11 0.00
Mon 08/31 17Z 0.07 3204  59  14  11 0.00
Mon 08/31 18Z 0.08 3103  59  14  11 0.00
Mon 08/31 19Z 0.13 3003  59  14  11 0.00
Mon 08/31 20Z 0.16 2904  56  14  11 0.00
Mon 08/31 21Z 0.10 2902  51  13  11 0.00
Mon 08/31 22Z 0.09 2802  47  13  11 0.00
Mon 08/31 23Z 0.07 3002  45  14  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.28 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