Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260619_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)
=== ===== === ==== ==== === === === ====
Fri 06/19 18Z 2.58 2617  84  57   9 0.00
Fri 06/19 19Z 11.53 2619  80  47   9 0.00
Fri 06/19 20Z 11.06 2622  78  50  10 0.00
Fri 06/19 21Z 12.42 2624  67  36  10 0.01
Fri 06/19 22Z 14.28 2627  69  52  10 0.00
Fri 06/19 23Z 9.08 2629  78  61   9 0.00
Sat 06/20 00Z 2.27 2729  85  59   8 0.00
Sat 06/20 01Z 1.74 2730  87  64   8 0.00
Sat 06/20 02Z 1.57 2730  89  67   8 0.01
Sat 06/20 03Z 1.46 2732  91  76   8 0.02
Sat 06/20 04Z 1.21 2731  91  79   8 0.03
Sat 06/20 05Z 1.05 2730  94  86   8 0.05
Sat 06/20 06Z 0.96 2730  96  93   8 0.07
Sat 06/20 07Z 0.89 2830  97  94   8 0.09
Sat 06/20 08Z 0.79 2828  97  93   8 0.09
Sat 06/20 09Z 0.66 2925  97  87   8 0.05
Sat 06/20 10Z 0.67 2926  97  81   7 0.04
Sat 06/20 11Z 0.67 2925  97  67   7 0.02
Sat 06/20 12Z 0.63 3024  95  66   7 0.01
Sat 06/20 13Z 0.70 3025  95  69   7 0.01
Sat 06/20 14Z 0.86 2924  94  69   8 0.01
Sat 06/20 15Z 1.20 2922  95  68   8 0.01
Sat 06/20 16Z 1.13 2921  96  77   8 0.03
Sat 06/20 17Z 1.11 3021  96  74   8 0.03
Sat 06/20 18Z 0.82 3021  95  66   8 0.03
Sat 06/20 19Z 0.79 3021  95  68   9 0.03
Sat 06/20 20Z 0.73 3020  92  72   9 0.01
Sat 06/20 21Z 0.68 3120  92  70   9 0.02
Sat 06/20 22Z 0.67 3018  93  69   9 0.01
Sat 06/20 23Z 0.52 3017  91  71   9 0.01
Sun 06/21 00Z 0.57 3017  89  65   9 0.01
Sun 06/21 01Z 0.44 3016  90  60   9 0.00
Sun 06/21 02Z 0.35 3015  89  58   9 0.00
Sun 06/21 03Z 0.31 3014  86  57  10 0.00
Sun 06/21 04Z 0.28 3014  86  59  10 0.00
Sun 06/21 05Z 0.27 3013  87  63   9 0.00
Sun 06/21 06Z 0.25 3012  88  67   9 0.00
Sun 06/21 07Z 0.20 3111  88  70   9 0.00
Sun 06/21 08Z 0.20 3111  88  69  10 0.00
Sun 06/21 09Z 0.21 3010  88  65  10 0.00
Sun 06/21 10Z 0.23 2809  89  61   9 0.00
Sun 06/21 11Z 0.22 2708  88  61  10 0.00
Sun 06/21 12Z 0.22 2607  86  67  10 0.00
Sun 06/21 13Z 0.23 2607  85  68  10 0.00
Sun 06/21 14Z 0.28 2608  86  72   9 0.00
Sun 06/21 15Z 0.35 2507  87  70   9 0.00
Sun 06/21 16Z 0.73 2508  88  69   9 0.00
Sun 06/21 17Z 2.69 2709  88  69   9 0.00
Sun 06/21 18Z 2.76 2708  87  72  10 0.02
Sun 06/21 19Z 0.99 2710  82  57  10 0.06
Sun 06/21 20Z 0.54 2808  81  42  10 0.01
Sun 06/21 21Z 0.51 2711  87  43  10 0.01
Sun 06/21 22Z 0.34 2811  77  49  10 0.01
Sun 06/21 23Z 0.36 2912  75  37  10 0.00
Mon 06/22 00Z 0.40 2913  81  41  10 0.00
Mon 06/22 01Z 0.43 2812  81  46  10 0.00
Mon 06/22 02Z 0.48 2813  85  49  10 0.00
Mon 06/22 03Z 0.43 2813  85  37  10 0.00
Mon 06/22 04Z 0.30 2911  79  30  10 0.00
Mon 06/22 05Z 0.25 2910  77  32  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.81 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