Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260621_0000
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 06/21 00Z 0.57 2913  92  80   9 0.00
Sun 06/21 01Z 0.64 2816  95  88   8 0.05
Sun 06/21 02Z 0.62 2918  95  91   8 0.08
Sun 06/21 03Z 0.66 2919  94  88   8 0.03
Sun 06/21 04Z 0.57 2918  92  91   8 0.01
Sun 06/21 05Z 0.54 2918  92  90   8 0.01
Sun 06/21 06Z 0.44 2916  87  86   8 0.00
Sun 06/21 07Z 0.45 2916  88  91   8 0.01
Sun 06/21 08Z 0.50 2816  91  88   8 0.01
Sun 06/21 09Z 0.43 2815  90  84   8 0.01
Sun 06/21 10Z 0.44 2816  89  78   8 0.00
Sun 06/21 11Z 0.44 2816  85  76   8 0.00
Sun 06/21 12Z 0.44 2917  88  75   8 0.00
Sun 06/21 13Z 0.43 2916  90  82   8 0.00
Sun 06/21 14Z 0.44 3014  92  77   8 0.00
Sun 06/21 15Z 0.77 2913  94  74   7 0.00
Sun 06/21 16Z 0.98 2812  96  79   8 0.00
Sun 06/21 17Z 0.75 2813  96  84   8 0.02
Sun 06/21 18Z 0.74 2813  95  82   8 0.03
Sun 06/21 19Z 0.81 2814  93  79   9 0.04
Sun 06/21 20Z 0.65 2914  91  67   9 0.02
Sun 06/21 21Z 0.80 2914  93  70   9 0.03
Sun 06/21 22Z 1.25 3014  90  71   9 0.02
Sun 06/21 23Z 0.70 3014  89  71   9 0.02
Mon 06/22 00Z 0.44 3013  89  64   9 0.02
Mon 06/22 01Z 0.49 3015  89  64   9 0.04
Mon 06/22 02Z 0.40 3014  87  60   9 0.00
Mon 06/22 03Z 0.29 3113  86  58   9 0.00
Mon 06/22 04Z 0.22 3111  83  58   9 0.00
Mon 06/22 05Z 0.19 3110  80  52   9 0.00
Mon 06/22 06Z 0.17 3108  78  51   9 0.00
Mon 06/22 07Z 0.18 3007  77  45   9 0.00
Mon 06/22 08Z 0.14 3006  76  39   9 0.00
Mon 06/22 09Z 0.15 2905  77  36   9 0.00
Mon 06/22 10Z 0.18 2805  77  34   9 0.00
Mon 06/22 11Z 0.21 2705  76  35   9 0.00
Mon 06/22 12Z 0.17 2804  72  35   9 0.00
Mon 06/22 13Z 0.09 2902  69  34   9 0.00
Mon 06/22 14Z 0.03 3000  71  32  10 0.00
Mon 06/22 15Z 0.09 1802  78  29   9 0.00
Mon 06/22 16Z 0.14 1804  83  28   9 0.00
Mon 06/22 17Z 0.24 1806  83  24  10 0.00
Mon 06/22 18Z 0.32 1908  82  28  10 0.01
Mon 06/22 19Z 0.27 1810  80  37  10 0.00
Mon 06/22 20Z 0.23 1910  87  74   9 0.02
Mon 06/22 21Z 0.11 1608  92  94   8 0.11
Mon 06/22 22Z 0.20 1412  91  96   8 0.10
Mon 06/22 23Z 0.28 1316  94  98   8 0.11
Tue 06/23 00Z 0.34 1318  93  99   8 0.11
Tue 06/23 01Z 0.36 1220  94  98   8 0.12
Tue 06/23 02Z 0.39 1222  95  97   9 0.10
Tue 06/23 03Z 0.35 1221  96  97   9 0.25
Tue 06/23 04Z 0.47 1225  97  95   9 0.22
Tue 06/23 05Z 0.42 1223  97  91   9 0.23
Tue 06/23 06Z 0.32 1318  97  94  10 0.16
Tue 06/23 07Z 0.24 1314  97  93  11 0.10
Tue 06/23 08Z 0.22 1310  98  93  11 0.07
Tue 06/23 09Z 0.16 1207  98  94  11 0.09
Tue 06/23 10Z 0.11 1404  98  92  11 0.07
Tue 06/23 11Z 0.10 1501  98  95  11 0.05

Run total areal avg QPF for the Central_Greens is: 2.37 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