NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260905_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)
=== ===== === ==== ==== === === === ====
Sat 09/05 18Z 0.11 3510  95  79  10 0.00
Sat 09/05 19Z 0.16 0010  96  84  10 0.06
Sat 09/05 20Z 0.13 3511  96  87  10 0.10
Sat 09/05 21Z 0.15 0012  96  83  10 0.04
Sat 09/05 22Z 0.22 0112  95  79  10 0.02
Sat 09/05 23Z 0.26 0212  93  76   9 0.02
Sun 09/06 00Z 0.32 0313  94  77   9 0.01
Sun 09/06 01Z 0.34 0313  96  80   9 0.00
Sun 09/06 02Z 0.41 0413  97  83   9 0.01
Sun 09/06 03Z 0.43 0713  95  88   9 0.02
Sun 09/06 04Z 0.44 0914  95  89   8 0.03
Sun 09/06 05Z 0.36 0911  96  90   8 0.03
Sun 09/06 06Z 0.28 1009  96  92   7 0.05
Sun 09/06 07Z 0.21 1007  97  92   7 0.02
Sun 09/06 08Z 0.16 0904  97  89   7 0.02
Sun 09/06 09Z 0.14 0604  98  82   7 0.01
Sun 09/06 10Z 0.14 0305  98  82   7 0.01
Sun 09/06 11Z 0.14 0208  97  82   6 0.01
Sun 09/06 12Z 0.13 0109  93  81   6 0.00
Sun 09/06 13Z 0.14 0110  91  78   6 0.00
Sun 09/06 14Z 0.18 0111  88  68   6 0.00
Sun 09/06 15Z 0.23 0112  89  55   6 0.00
Sun 09/06 16Z 0.41 0011  91  42   6 0.00
Sun 09/06 17Z 0.40 0010  91  39   7 0.00
Sun 09/06 18Z 0.13 3510  91  38   7 0.00
Sun 09/06 19Z 0.11 3511  92  32   7 0.00
Sun 09/06 20Z 0.17 3412  92  26   7 0.00
Sun 09/06 21Z 0.13 3412  91  22   7 0.00
Sun 09/06 22Z 0.07 3412  86  16   7 0.00
Sun 09/06 23Z 0.07 3415  80   9   7 0.00
Mon 09/07 00Z 0.11 3417  78   7   7 0.00
Mon 09/07 01Z 0.19 3319  82  21   7 0.00
Mon 09/07 02Z 0.34 3220  87  27   7 0.00
Mon 09/07 03Z 0.32 3221  91  51   7 0.03
Mon 09/07 04Z 0.22 3322  91  49   7 0.01
Mon 09/07 05Z 0.11 3421  89  19   7 0.01
Mon 09/07 06Z 0.04 3420  86   6   7 0.01
Mon 09/07 07Z 0.04 3419  84   6   7 0.00
Mon 09/07 08Z 0.03 3518  80   7   7 0.00
Mon 09/07 09Z 0.06 3419  77   7   7 0.00
Mon 09/07 10Z 0.08 3419  73   6   7 0.00
Mon 09/07 11Z 0.13 3419  73   7   7 0.00
Mon 09/07 12Z 0.18 3320  76   8   7 0.00
Mon 09/07 13Z 0.20 3320  76  11   7 0.00
Mon 09/07 14Z 0.26 3321  77  12   7 0.00
Mon 09/07 15Z 0.30 3320  78  12   7 0.00
Mon 09/07 16Z 1.09 3318  80  10   7 0.00
Mon 09/07 17Z 3.02 3217  83   8   7 0.00
Mon 09/07 18Z 3.36 3215  84   7   7 0.00
Mon 09/07 19Z 2.48 3113  84   7   7 0.00
Mon 09/07 20Z 1.77 3114  82   7   8 0.00
Mon 09/07 21Z 0.90 3115  81   9   8 0.00
Mon 09/07 22Z 0.91 3017  84  15   8 0.00
Mon 09/07 23Z 0.70 3018  82  30   8 0.00
Tue 09/08 00Z 0.56 3018  83  48   9 0.00
Tue 09/08 01Z 0.44 3119  84  58   9 0.00
Tue 09/08 02Z 0.32 3119  81  45   9 0.00
Tue 09/08 03Z 0.27 3220  78  49  10 0.00
Tue 09/08 04Z 0.25 3221  79  67  10 0.00
Tue 09/08 05Z 0.23 3221  78  65  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.52 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