NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260813_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)
=== ===== === ==== ==== === === === ====
Thu 08/13 18Z 0.54 3208  88  75  12 0.00
Thu 08/13 19Z 0.81 3108  85  82  12 0.02
Thu 08/13 20Z 0.57 3108  82  84  12 0.01
Thu 08/13 21Z 0.32 3109  81  80  12 0.00
Thu 08/13 22Z 0.27 3210  79  73  12 0.06
Thu 08/13 23Z 0.39 3111  79  53  12 0.00
Fri 08/14 00Z 0.51 2913  82  43  12 0.00
Fri 08/14 01Z 0.63 2816  90  52  12 0.00
Fri 08/14 02Z 0.57 3020  91  66  11 0.02
Fri 08/14 03Z 0.31 3220  91  71  11 0.01
Fri 08/14 04Z 0.20 3320  83  61  11 0.01
Fri 08/14 05Z 0.24 3219  81  51  10 0.00
Fri 08/14 06Z 0.23 3219  79  45  10 0.00
Fri 08/14 07Z 0.20 3219  76  40  10 0.00
Fri 08/14 08Z 0.19 3320  76  34  10 0.00
Fri 08/14 09Z 0.20 3321  76  30  10 0.00
Fri 08/14 10Z 0.21 3221  75  29  10 0.00
Fri 08/14 11Z 0.22 3221  74  35  10 0.00
Fri 08/14 12Z 0.22 3221  73  38   9 0.00
Fri 08/14 13Z 0.19 3319  73  43   9 0.00
Fri 08/14 14Z 0.20 3218  76  45   9 0.00
Fri 08/14 15Z 0.19 3316  75  53   8 0.00
Fri 08/14 16Z 0.23 3316  71  68   8 0.00
Fri 08/14 17Z 0.60 3315  70  58   8 0.00
Fri 08/14 18Z 1.51 3214  68  55   8 0.00
Fri 08/14 19Z 1.80 3114  70  53   8 0.00
Fri 08/14 20Z 1.37 3015  76  52   9 0.00
Fri 08/14 21Z 0.86 3015  80  44   9 0.00
Fri 08/14 22Z 0.67 3115  77  36   9 0.00
Fri 08/14 23Z 0.51 3217  74  29   9 0.00
Sat 08/15 00Z 0.43 3218  74  19   8 0.00
Sat 08/15 01Z 0.37 3319  76  12   8 0.00
Sat 08/15 02Z 0.17 3419  76   9   8 0.00
Sat 08/15 03Z 0.24 3319  77   9   8 0.00
Sat 08/15 04Z 0.06 3418  73   7   8 0.00
Sat 08/15 05Z 0.04 3416  73   8   8 0.00
Sat 08/15 06Z 0.09 3414  72  10   8 0.00
Sat 08/15 07Z 0.16 3313  69  10   8 0.00
Sat 08/15 08Z 0.19 3314  68  10   8 0.00
Sat 08/15 09Z 0.18 3316  67   8   8 0.00
Sat 08/15 10Z 0.15 3319  70   8   8 0.00
Sat 08/15 11Z 0.12 3420  70  10   7 0.00
Sat 08/15 12Z 0.08 3421  71  13   7 0.00
Sat 08/15 13Z 0.08 3416  69  13   8 0.00
Sat 08/15 14Z 0.12 3311  74  13   7 0.00
Sat 08/15 15Z 0.32 3210  79  17   7 0.00
Sat 08/15 16Z 0.34 3211  76  15   7 0.00
Sat 08/15 17Z 0.65 3213  71  15   7 0.00
Sat 08/15 18Z 0.76 3314  67  13   8 0.00
Sat 08/15 19Z 0.74 3314  66  13   8 0.00
Sat 08/15 20Z 0.40 3312  63  15   8 0.00
Sat 08/15 21Z 0.24 3310  60  15   9 0.00
Sat 08/15 22Z 0.05 3409  54  12   9 0.00
Sat 08/15 23Z 0.03 3507  50  11  10 0.00
Sun 08/16 00Z 0.04 3406  48  12  10 0.00
Sun 08/16 01Z 0.10 3207  45  13  10 0.00
Sun 08/16 02Z 0.07 3307  44  13  10 0.00
Sun 08/16 03Z 0.11 3207  48  12  10 0.00
Sun 08/16 04Z 0.11 3207  54  12   9 0.00
Sun 08/16 05Z 0.10 3106  59  12  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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