Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260207_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)
=== ===== === ==== ==== === === === ====
Sat 02/07 00Z 0.10 1810  82  77 -11 0.00
Sat 02/07 01Z 0.21 1912  85  79 -11 0.00
Sat 02/07 02Z 0.30 2013  88  85 -12 0.00
Sat 02/07 03Z 0.32 2112  89  87 -12 0.00
Sat 02/07 04Z 0.36 2112  88  86 -12 0.00
Sat 02/07 05Z 0.31 2111  89  85 -12 0.01
Sat 02/07 08Z 0.14 2205  91  84 -12 0.01
Sat 02/07 09Z 0.09 2103  91  83 -12 0.01
Sat 02/07 10Z 0.07 2302  92  84 -12 0.01
Sat 02/07 11Z 0.07 2802  92  84 -12 0.01
Sat 02/07 12Z 0.07 3306  91  81 -13 0.01
Sat 02/07 13Z 0.14 3410  90  81 -14 0.02
Sat 02/07 14Z 0.07 3414  89  81 -15 0.03
Sat 02/07 15Z 0.07 3315  86  82 -16 0.02
Sat 02/07 16Z 0.09 3317  84  82 -17 0.01
Sat 02/07 17Z 0.11 3319  83  82 -18 0.01
Sat 02/07 18Z 0.12 3320  82  82 -18 0.01
Sat 02/07 19Z 0.12 3320  83  82 -19 0.01
Sat 02/07 20Z 0.13 3322  83  82 -19 0.01
Sat 02/07 21Z 0.14 3323  83  80 -20 0.01
Sat 02/07 22Z 0.13 3324  83  80 -20 0.00
Sat 02/07 23Z 0.13 3325  83  80 -21 0.00
Sun 02/08 00Z 0.13 3325  83  80 -21 0.00
Sun 02/08 01Z 0.11 3325  83  79 -20 0.00
Sun 02/08 02Z 0.09 3325  85  77 -20 0.00
Sun 02/08 03Z 0.09 3324  85  75 -20 0.00
Sun 02/08 04Z 0.08 3324  84  74 -20 0.00
Sun 02/08 05Z 0.07 3323  83  74 -19 0.00
Sun 02/08 06Z 0.07 3323  83  76 -19 0.00
Sun 02/08 07Z 0.08 3323  83  79 -19 0.00
Sun 02/08 08Z 0.07 3324  81  81 -19 0.00
Sun 02/08 09Z 0.05 3424  79  82 -18 0.00
Sun 02/08 10Z 0.03 3425  80  80 -18 0.00
Sun 02/08 11Z 0.02 3426  81  79 -17 0.00
Sun 02/08 12Z 0.03 3526  81  80 -17 0.00
Sun 02/08 13Z 0.02 3527  76  67 -16 0.00
Sun 02/08 14Z 0.03 3527  68  44 -16 0.00
Sun 02/08 15Z 0.02 3526  64  29 -15 0.00
Sun 02/08 16Z 0.02 3426  64  42 -15 0.00
Sun 02/08 17Z 0.02 3426  62  38 -14 0.00
Sun 02/08 18Z 0.03 3426  60  46 -13 0.00
Sun 02/08 19Z 0.04 3426  59  39 -13 0.00
Sun 02/08 20Z 0.05 3428  57  31 -12 0.00
Sun 02/08 21Z 0.06 3430  53  31 -12 0.00
Sun 02/08 22Z 0.05 3431  50  35 -11 0.00
Sun 02/08 23Z 0.03 3431  47  31 -11 0.00
Mon 02/09 00Z 0.03 3431  44  30 -11 0.00
Mon 02/09 01Z 0.03 3431  44  22 -11 0.00
Mon 02/09 02Z 0.05 3430  49  32 -12 0.00
Mon 02/09 03Z 0.07 3429  56  36 -12 0.00
Mon 02/09 04Z 0.09 3329  65  33 -12 0.00
Mon 02/09 05Z 0.11 3330  68  29 -12 0.00
Mon 02/09 06Z 0.12 3330  67  29 -12 0.00
Mon 02/09 07Z 0.11 3330  64  26 -12 0.00
Mon 02/09 08Z 0.10 3331  63  19 -12 0.00
Mon 02/09 09Z 0.09 3330  58   9 -12 0.00
Mon 02/09 10Z 0.08 3329  56   4 -12 0.00
Mon 02/09 11Z 0.10 3329  53   8 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.19 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