Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260206_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)
=== ===== === ==== ==== === === === ====
Fri 02/06 00Z 0.08 3105  58  21 -10 0.00
Fri 02/06 01Z 0.05 3205  59  22 -10 0.00
Fri 02/06 02Z 0.05 3204  63  22 -11 0.00
Fri 02/06 03Z 0.02 3302  66  20 -11 0.00
Fri 02/06 04Z 0.02 0101  64  18 -11 0.00
Fri 02/06 05Z 0.03 0701  59  17 -10 0.00
Fri 02/06 06Z 0.03 1302  54  15 -10 0.00
Fri 02/06 07Z 0.02 1605  50  13 -10 0.00
Fri 02/06 08Z 0.02 1608  53   9 -10 0.00
Fri 02/06 09Z 0.02 1709  56   5 -11 0.00
Fri 02/06 10Z 0.05 1809  58   4 -11 0.00
Fri 02/06 11Z 0.05 1810  61  13 -11 0.00
Fri 02/06 12Z 0.05 1811  64  41 -12 0.00
Fri 02/06 13Z 0.07 1812  68  70 -12 0.00
Fri 02/06 14Z 0.12 1914  72  84 -12 0.00
Fri 02/06 15Z 0.14 1913  75  84 -12 0.00
Fri 02/06 16Z 0.16 1911  76  86 -11 0.00
Fri 02/06 17Z 0.17 1910  76  87 -11 0.00
Fri 02/06 18Z 0.17 1908  77  86 -11 0.00
Fri 02/06 19Z 0.25 1907  81  88 -11 0.00
Fri 02/06 20Z 0.12 1807  84  91 -11 0.00
Fri 02/06 21Z 0.07 1707  87  89 -11 0.00
Fri 02/06 22Z 0.09 1808  87  85 -11 0.00
Fri 02/06 23Z 0.11 1809  88  85 -11 0.00
Sat 02/07 00Z 0.11 1810  89  88 -11 0.00
Sat 02/07 01Z 0.14 1911  93  90 -11 0.00
Sat 02/07 02Z 0.18 1912  94  87 -11 0.00
Sat 02/07 03Z 0.21 1913  93  87 -11 0.01
Sat 02/07 04Z 0.21 1913  92  87 -11 0.01
Sat 02/07 05Z 0.20 1913  92  86 -11 0.02
Sat 02/07 06Z 0.19 1913  92  85 -11 0.02
Sat 02/07 07Z 0.17 1912  92  85 -11 0.02
Sat 02/07 08Z 0.17 1911  92  84 -11 0.02
Sat 02/07 09Z 0.17 2009  92  84 -11 0.01
Sat 02/07 10Z 0.15 2006  92  84 -12 0.01
Sat 02/07 11Z 0.14 2304  92  84 -12 0.01
Sat 02/07 12Z 0.10 3204  92  83 -12 0.02
Sat 02/07 13Z 0.06 3408  90  82 -13 0.02
Sat 02/07 14Z 0.06 3512  88  82 -13 0.02
Sat 02/07 15Z 0.03 3414  87  82 -14 0.01
Sat 02/07 16Z 0.04 3415  86  82 -14 0.01
Sat 02/07 17Z 0.05 3415  84  83 -15 0.01
Sat 02/07 18Z 0.06 3317  84  83 -16 0.01
Sat 02/07 19Z 0.08 3319  83  82 -17 0.01
Sat 02/07 20Z 0.10 3322  83  81 -17 0.01
Sat 02/07 21Z 0.10 3323  85  80 -18 0.00
Sat 02/07 22Z 0.09 3325  85  77 -18 0.00
Sat 02/07 23Z 0.09 3327  85  74 -19 0.00
Sun 02/08 00Z 0.09 3328  84  72 -19 0.00
Sun 02/08 01Z 0.10 3329  84  72 -19 0.00
Sun 02/08 02Z 0.11 3328  83  71 -19 0.00
Sun 02/08 03Z 0.12 3327  82  73 -20 0.00
Sun 02/08 04Z 0.12 3326  81  73 -19 0.00
Sun 02/08 05Z 0.11 3326  81  73 -19 0.00
Sun 02/08 06Z 0.12 3326  80  68 -19 0.00
Sun 02/08 07Z 0.13 3326  79  62 -20 0.00
Sun 02/08 08Z 0.14 3327  78  58 -20 0.00
Sun 02/08 09Z 0.16 3229  76  54 -21 0.00
Sun 02/08 10Z 0.16 3231  72  49 -21 0.00
Sun 02/08 11Z 0.15 3331  69  33 -21 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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