NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260530_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 05/30 12Z 0.69 0324  98  90  -1 0.00
Sat 05/30 13Z 0.75 0324  99  61  -1 0.07
Sat 05/30 14Z 0.62 0219  96  32  -1 0.03
Sat 05/30 15Z 0.65 0218  94  30  -1 0.01
Sat 05/30 16Z 0.98 0215  95  39   0 0.01
Sat 05/30 17Z 0.89 0115  91  48   0 0.01
Sat 05/30 18Z 0.62 0015  88  48   0 0.00
Sat 05/30 19Z 1.18 0016  86  51   0 0.00
Sat 05/30 20Z 2.50 0017  81  51   0 0.00
Sat 05/30 21Z 3.07 0117  75  51   0 0.00
Sat 05/30 22Z 2.81 0117  70  50   1 0.00
Sat 05/30 23Z 1.66 0116  69  57   1 0.00
Sun 05/31 00Z 0.83 0117  70  54   1 0.00
Sun 05/31 01Z 0.62 0218  69  49   1 0.00
Sun 05/31 02Z 0.51 0119  65  35   1 0.00
Sun 05/31 03Z 0.48 0119  61  22   2 0.00
Sun 05/31 04Z 0.40 0119  59  14   2 0.00
Sun 05/31 05Z 0.30 0018  58  11   2 0.00
Sun 05/31 06Z 0.22 0018  60  10   2 0.00
Sun 05/31 07Z 0.18 0018  65  12   2 0.00
Sun 05/31 08Z 0.11 3516  70  14   3 0.00
Sun 05/31 09Z 0.09 3415  70  15   3 0.00
Sun 05/31 10Z 0.18 3314  71  19   3 0.00
Sun 05/31 11Z 0.27 3215  69  24   3 0.00
Sun 05/31 12Z 0.34 3116  67  23   4 0.00
Sun 05/31 13Z 0.39 3115  68  40   4 0.00
Sun 05/31 14Z 0.60 3015  68  60   4 0.00
Sun 05/31 15Z 1.33 3117  68  77   4 0.00
Sun 05/31 16Z 3.50 3117  69  81   4 0.00
Sun 05/31 17Z 2.69 3115  73  83   4 0.00
Sun 05/31 18Z 0.88 3013  81  85   4 0.02
Sun 05/31 19Z 0.87 2915  85  92   4 0.01
Sun 05/31 20Z 0.67 2916  80  86   5 0.02
Sun 05/31 21Z 0.90 2815  79  73   5 0.00
Sun 05/31 22Z 1.28 2819  83  85   5 0.01
Sun 05/31 23Z 1.13 3021  80  94   4 0.02
Mon 06/01 00Z 0.60 3122  87  96   4 0.05
Mon 06/01 01Z 0.53 3122  80  90   4 0.03
Mon 06/01 02Z 0.60 3121  76  78   4 0.00
Mon 06/01 03Z 0.55 3121  78  58   4 0.00
Mon 06/01 04Z 0.31 3318  83  49   3 0.00
Mon 06/01 05Z 0.14 3314  84  48   3 0.00
Mon 06/01 06Z 0.16 3313  81  58   3 0.00
Mon 06/01 07Z 0.08 3411  81  67   3 0.00
Mon 06/01 08Z 0.09 0009  83  75   3 0.00
Mon 06/01 09Z 0.09 0008  83  70   2 0.00
Mon 06/01 10Z 0.14 0108  84  64   2 0.00
Mon 06/01 11Z 0.19 0309  89  72   2 0.00
Mon 06/01 12Z 0.26 0409  93  80   1 0.00
Mon 06/01 13Z 0.27 0608  96  82   1 0.00
Mon 06/01 14Z 0.30 0708  96  79   1 0.00
Mon 06/01 15Z 0.38 0909  96  73   1 0.00
Mon 06/01 16Z 0.43 0909  95  67   0 0.00
Mon 06/01 17Z 0.63 0807  93  66   0 0.00
Mon 06/01 18Z 1.00 0505  88  58   1 0.00
Mon 06/01 19Z 1.43 0305  84  46   2 0.00
Mon 06/01 20Z 1.46 0206  82  42   2 0.00
Mon 06/01 21Z 1.08 0205  82  51   3 0.00
Mon 06/01 22Z 0.46 0105  82  58   3 0.01
Mon 06/01 23Z 0.14 0005  83  47   3 0.01

Run total areal avg QPF for the Central_Greens is: 0.31 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