Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260620_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 06/20 12Z 0.95 2924  96  90   7 0.00
Sat 06/20 13Z 0.90 3026  98  90   7 0.02
Sat 06/20 14Z 0.90 3026  98  93   7 0.04
Sat 06/20 15Z 0.83 2925  97  92   8 0.03
Sat 06/20 16Z 0.81 3024  97  92   8 0.03
Sat 06/20 17Z 0.66 3021  97  90   9 0.04
Sat 06/20 18Z 0.69 3021  96  90   9 0.07
Sat 06/20 19Z 0.74 3021  96  84   9 0.10
Sat 06/20 20Z 0.93 3020  95  77   9 0.07
Sat 06/20 21Z 0.94 3019  94  79   9 0.12
Sat 06/20 22Z 0.82 2920  94  76   9 0.07
Sat 06/20 23Z 0.73 2921  92  68   9 0.07
Sun 06/21 00Z 0.76 2921  93  65   9 0.01
Sun 06/21 01Z 0.76 2921  92  65   9 0.00
Sun 06/21 02Z 0.62 2920  92  64   9 0.00
Sun 06/21 03Z 0.49 3018  92  65   9 0.00
Sun 06/21 04Z 0.47 2917  95  67   8 0.01
Sun 06/21 05Z 0.40 3015  94  72   8 0.01
Sun 06/21 06Z 0.34 3014  94  78   8 0.01
Sun 06/21 07Z 0.32 3013  95  76   8 0.01
Sun 06/21 08Z 0.33 3013  96  72   8 0.01
Sun 06/21 09Z 0.33 3013  95  61   8 0.01
Sun 06/21 10Z 0.30 3012  93  51   8 0.01
Sun 06/21 11Z 0.30 2912  92  52   8 0.00
Sun 06/21 12Z 0.29 2911  92  61   8 0.00
Sun 06/21 13Z 0.31 2911  92  73   8 0.00
Sun 06/21 14Z 0.30 2910  91  75   8 0.00
Sun 06/21 15Z 0.34 2909  91  73   8 0.00
Sun 06/21 16Z 0.74 2909  92  74   8 0.00
Sun 06/21 17Z 0.77 3009  92  71   8 0.00
Sun 06/21 18Z 0.67 3009  92  68   8 0.00
Sun 06/21 19Z 0.48 3009  92  67   9 0.00
Sun 06/21 20Z 0.40 3009  92  71   9 0.04
Sun 06/21 21Z 0.27 3110  87  65   9 0.02
Sun 06/21 22Z 0.22 3210  85  55  10 0.01
Sun 06/21 23Z 0.25 3110  86  55  10 0.00
Mon 06/22 00Z 0.29 3011  87  58   9 0.00
Mon 06/22 01Z 0.27 3112  86  57   9 0.00
Mon 06/22 02Z 0.28 3112  85  58   9 0.00
Mon 06/22 03Z 0.24 3111  87  50   9 0.00
Mon 06/22 04Z 0.15 3210  84  40  10 0.00
Mon 06/22 05Z 0.04 3408  77  31  10 0.00
Mon 06/22 06Z 0.04 3306  76  31  10 0.00
Mon 06/22 07Z 0.09 3105  80  38  10 0.00
Mon 06/22 08Z 0.12 2804  83  41   9 0.00
Mon 06/22 09Z 0.13 2503  85  38   9 0.00
Mon 06/22 10Z 0.11 2403  83  26   9 0.00
Mon 06/22 11Z 0.05 2002  79  22   9 0.00
Mon 06/22 12Z 0.02 1703  77  22  10 0.00
Mon 06/22 13Z 0.04 1706  78  22  10 0.00
Mon 06/22 14Z 0.10 1810  79  30  10 0.00
Mon 06/22 15Z 0.07 1712  79  89   9 0.00
Mon 06/22 16Z 0.09 1712  86  94   8 0.02
Mon 06/22 17Z 0.07 1611  88  81   8 0.04
Mon 06/22 18Z 0.13 1515  87  76   8 0.03
Mon 06/22 19Z 0.39 1420  88  98   8 0.03
Mon 06/22 20Z 0.79 1221  96  99   8 0.11
Mon 06/22 21Z 0.71 1225  98  99   9 0.28
Mon 06/22 22Z 0.56 1226  98  99   9 0.25
Mon 06/22 23Z 0.41 1325  98  98  10 0.20

Run total areal avg QPF for the Central_Greens is: 1.77 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